Delete `TxBuilder::subtract_non_htlc_outputs`

diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index d09e117..104e61a 100644
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -71,7 +71,10 @@ use crate::ln::types::ChannelId;
 use crate::offers::static_invoice::StaticInvoice;
 use crate::routing::gossip::NodeId;
 use crate::sign::ecdsa::EcdsaChannelSigner;
-use crate::sign::tx_builder::{ChannelStats, HTLCAmountDirection, SpecTxBuilder, TxBuilder};
+use crate::sign::tx_builder::{
+	saturating_sub_anchor_outputs, ChannelStats, HTLCAmountDirection, SpecTxBuilder,
+	TxBuilder,
+};
 use crate::sign::{ChannelSigner, EntropySource, NodeSigner, Recipient, SignerProvider};
 use crate::types::features::{ChannelTypeFeatures, InitFeatures};
 use crate::types::payment::{PaymentHash, PaymentPreimage};
@@ -5914,8 +5917,8 @@ impl<SP: SignerProvider> ChannelContext<SP> {
 		);
 		let htlc_stats = context.get_pending_htlc_stats(funding, None, dust_exposure_limiting_feerate);
 
-		// Subtract any non-HTLC outputs from the local and remote balances
-		let (local_balance_before_fee_msat, remote_balance_before_fee_msat) = SpecTxBuilder {}.subtract_non_htlc_outputs(
+		// Subtract anchor outputs from the local and remote balances
+		let (local_balance_before_fee_msat, remote_balance_before_fee_msat) = saturating_sub_anchor_outputs(
 			funding.is_outbound(),
 			funding.value_to_self_msat.saturating_sub(htlc_stats.pending_outbound_htlcs_value_msat),
 			(funding.get_value_satoshis() * 1000).checked_sub(funding.value_to_self_msat).unwrap().saturating_sub(htlc_stats.pending_inbound_htlcs_value_msat),
diff --git a/lightning/src/sign/tx_builder.rs b/lightning/src/sign/tx_builder.rs
index 3b34fb8..9c2942f 100644
--- a/lightning/src/sign/tx_builder.rs
+++ b/lightning/src/sign/tx_builder.rs
@@ -117,7 +117,7 @@ fn commit_plus_htlc_tx_fees_msat(
 	(total_fees_msat, extra_accepted_htlc_total_fees_msat)
 }
 
-fn subtract_addl_outputs(
+pub(crate) fn checked_sub_anchor_outputs(
 	is_outbound_from_holder: bool, value_to_self_after_htlcs_msat: u64,
 	value_to_remote_after_htlcs_msat: u64, channel_type: &ChannelTypeFeatures,
 ) -> Result<(u64, u64), ()> {
@@ -127,13 +127,6 @@ fn subtract_addl_outputs(
 		0
 	};
 
-	// We MUST use checked subs here, as the funder's balance is not guaranteed to be greater
-	// than or equal to `total_anchors_sat`.
-	//
-	// This is because when the remote party sends an `update_fee` message, we build the new
-	// commitment transaction *before* checking whether the remote party's balance is enough to
-	// cover the total anchor sum.
-
 	if is_outbound_from_holder {
 		Ok((
 			value_to_self_after_htlcs_msat.checked_sub(total_anchors_sat * 1000).ok_or(())?,
@@ -147,6 +140,29 @@ fn subtract_addl_outputs(
 	}
 }
 
+pub(crate) fn saturating_sub_anchor_outputs(
+	is_outbound_from_holder: bool, value_to_self_after_htlcs: u64,
+	value_to_remote_after_htlcs: u64, channel_type: &ChannelTypeFeatures,
+) -> (u64, u64) {
+	let total_anchors_sat = if channel_type.supports_anchors_zero_fee_htlc_tx() {
+		ANCHOR_OUTPUT_VALUE_SATOSHI * 2
+	} else {
+		0
+	};
+
+	if is_outbound_from_holder {
+		(
+			value_to_self_after_htlcs.saturating_sub(total_anchors_sat * 1000),
+			value_to_remote_after_htlcs,
+		)
+	} else {
+		(
+			value_to_self_after_htlcs,
+			value_to_remote_after_htlcs.saturating_sub(total_anchors_sat * 1000),
+		)
+	}
+}
+
 fn get_dust_buffer_feerate(feerate_per_kw: u32) -> u32 {
 	// When calculating our exposure to dust HTLCs, we assume that the channel feerate
 	// may, at any point, increase by at least 10 sat/vB (i.e 2530 sat/kWU) or 25%,
@@ -192,8 +208,16 @@ fn get_next_commitment_stats(
 		value_to_counterparty_msat.checked_sub(inbound_htlcs_value_msat).ok_or(())?;
 
 	// Subtract the anchors from the channel funder
+
+	// We MUST use checked subs here, as the funder's balance is not guaranteed to be greater
+	// than or equal to `total_anchors_sat`.
+	//
+	// This is because when the remote party sends an `update_fee` message, we build the new
+	// commitment transaction *before* checking whether the remote party's balance is enough to
+	// cover the total anchor sum.
+
 	let (holder_balance_before_fee_msat, counterparty_balance_before_fee_msat) =
-		subtract_addl_outputs(
+		checked_sub_anchor_outputs(
 			is_outbound_from_holder,
 			value_to_holder_after_htlcs_msat,
 			value_to_counterparty_after_htlcs_msat,
@@ -270,10 +294,6 @@ pub(crate) trait TxBuilder {
 		dust_exposure_limiting_feerate: Option<u32>, broadcaster_dust_limit_satoshis: u64,
 		channel_type: &ChannelTypeFeatures,
 	) -> Result<ChannelStats, ()>;
-	fn subtract_non_htlc_outputs(
-		&self, is_outbound_from_holder: bool, value_to_self_after_htlcs: u64,
-		value_to_remote_after_htlcs: u64, channel_type: &ChannelTypeFeatures,
-	) -> (u64, u64);
 	fn build_commitment_transaction<L: Logger>(
 		&self, local: bool, commitment_number: u64, per_commitment_point: &PublicKey,
 		channel_parameters: &ChannelTransactionParameters, secp_ctx: &Secp256k1<secp256k1::All>,
@@ -307,36 +327,6 @@ impl TxBuilder for SpecTxBuilder {
 
 		Ok(ChannelStats { commitment_stats })
 	}
-	fn subtract_non_htlc_outputs(
-		&self, is_outbound_from_holder: bool, value_to_self_after_htlcs: u64,
-		value_to_remote_after_htlcs: u64, channel_type: &ChannelTypeFeatures,
-	) -> (u64, u64) {
-		let total_anchors_sat = if channel_type.supports_anchors_zero_fee_htlc_tx() {
-			ANCHOR_OUTPUT_VALUE_SATOSHI * 2
-		} else {
-			0
-		};
-
-		let mut local_balance_before_fee_msat = value_to_self_after_htlcs;
-		let mut remote_balance_before_fee_msat = value_to_remote_after_htlcs;
-
-		// We MUST use saturating subs here, as the funder's balance is not guaranteed to be greater
-		// than or equal to `total_anchors_sat`.
-		//
-		// This is because when the remote party sends an `update_fee` message, we build the new
-		// commitment transaction *before* checking whether the remote party's balance is enough to
-		// cover the total anchor sum.
-
-		if is_outbound_from_holder {
-			local_balance_before_fee_msat =
-				local_balance_before_fee_msat.saturating_sub(total_anchors_sat * 1000);
-		} else {
-			remote_balance_before_fee_msat =
-				remote_balance_before_fee_msat.saturating_sub(total_anchors_sat * 1000);
-		}
-
-		(local_balance_before_fee_msat, remote_balance_before_fee_msat)
-	}
 	fn build_commitment_transaction<L: Logger>(
 		&self, local: bool, commitment_number: u64, per_commitment_point: &PublicKey,
 		channel_parameters: &ChannelTransactionParameters, secp_ctx: &Secp256k1<secp256k1::All>,
@@ -402,8 +392,16 @@ impl TxBuilder for SpecTxBuilder {
 			.unwrap()
 			.checked_sub(remote_htlc_total_msat)
 			.unwrap();
-		let (local_balance_before_fee_msat, remote_balance_before_fee_msat) = self
-			.subtract_non_htlc_outputs(
+
+		// We MUST use saturating subs here, as the funder's balance is not guaranteed to be greater
+		// than or equal to `total_anchors_sat`.
+		//
+		// This is because when the remote party sends an `update_fee` message, we build the new
+		// commitment transaction *before* checking whether the remote party's balance is enough to
+		// cover the total anchor sum.
+
+		let (local_balance_before_fee_msat, remote_balance_before_fee_msat) =
+			saturating_sub_anchor_outputs(
 				channel_parameters.is_outbound_from_holder,
 				value_to_self_after_htlcs_msat,
 				value_to_remote_after_htlcs_msat,