lnutil.ChannelType: rm "discard unknown" part from discard_unknown_and_check

diff --git a/electrum/lnpeer.py b/electrum/lnpeer.py
index 6d8886d..6e62455 100644
--- a/electrum/lnpeer.py
+++ b/electrum/lnpeer.py
@@ -1007,6 +1007,7 @@ class Peer(Logger, EventListener):
             our_channel_type |= ChannelType(ChannelType.OPTION_ZEROCONF)
         # We do not set the option_scid_alias bit in channel_type because LND rejects it.
         # Eclair accepts channel_type with that bit, but does not require it.
+        assert our_channel_type.complies_with_features(self.features), f"{our_channel_type=!r}, {self.features=!r}"
 
         # if option_channel_type is negotiated: MUST set channel_type
         # if it includes channel_type: MUST set it to a defined type representing the type it wants.
@@ -1092,9 +1093,11 @@ class Peer(Logger, EventListener):
         their_channel_type = accept_channel_tlvs.get('channel_type')
         if their_channel_type is None:
             raise Exception("channel_type MUST be present in accept_channel, but missing")
-        their_channel_type = ChannelType.from_bytes(their_channel_type['type'], byteorder='big').discard_unknown_and_check()
+        their_channel_type = ChannelType.from_bytes(their_channel_type['type'], byteorder='big')
+        # if channel_type does not match the channel_type from open_channel:
+        #     MUST fail the channel.
         if their_channel_type != our_channel_type:
-            raise Exception("channel_type is not the one that we sent.")
+            raise Exception(f"channel_type is not the one that we sent. {our_channel_type=}. {their_channel_type=}.")
 
         remote_config = RemoteConfig(
             payment_basepoint=OnlyPubkeyKeypair(payload['payment_basepoint']),
@@ -1243,7 +1246,7 @@ class Peer(Logger, EventListener):
         if channel_type is None:
             raise Exception("channel_type MUST be present in open_channel, but missing")
         # MUST fail the channel if channel_type is not suitable.
-        channel_type = ChannelType.from_bytes(channel_type['type'], byteorder='big').discard_unknown_and_check()
+        channel_type = ChannelType.from_bytes(channel_type['type'], byteorder='big')
         if not channel_type.complies_with_features(self.features):
             raise Exception("sender has sent a channel type we don't support")
         assert channel_type & ChannelType.OPTION_STATIC_REMOTEKEY, "new legacy channel?!"
diff --git a/electrum/lnutil.py b/electrum/lnutil.py
index 962bac3..bb992db 100644
--- a/electrum/lnutil.py
+++ b/electrum/lnutil.py
@@ -1622,21 +1622,6 @@ class ChannelType(IntFlag):
     OPTION_SCID_ALIAS = 1 << 46  # variation flag
     OPTION_ZEROCONF = 1 << 50    # variation flag
 
-    def discard_unknown_and_check(self) -> 'ChannelType':
-        """Discards unknown flags and checks flag combination."""
-        flags = list_enabled_bits(self)
-        known_channel_types = []
-        for flag in flags:
-            channel_type = ChannelType(1 << flag)
-            if channel_type.name:
-                known_channel_types.append(channel_type)
-        final_channel_type = known_channel_types[0]
-        for channel_type in known_channel_types[1:]:
-            final_channel_type |= channel_type
-
-        final_channel_type.check_combinations()
-        return final_channel_type
-
     def check_combinations(self):
         """Raises if invalid flag combination."""
         basic_type = self & ~(ChannelType.OPTION_SCID_ALIAS | ChannelType.OPTION_ZEROCONF)
@@ -1644,7 +1629,7 @@ class ChannelType(IntFlag):
                 ChannelType.OPTION_STATIC_REMOTEKEY,
                 ChannelType.OPTION_ANCHORS | ChannelType.OPTION_STATIC_REMOTEKEY
         ]:
-            raise ValueError("Channel type is not a valid flag combination.")
+            raise ValueError(f"Channel type is not a valid flag combination: {self}")
 
     def complies_with_features(self, peer_features: LnFeatures) -> bool:
         """Returns whether channel_type complies with peer_features.
@@ -1655,6 +1640,7 @@ class ChannelType(IntFlag):
               For example, even if opt_anchors is a negotiated peer_feature, (as per my reading of BOLT-02),
               it is still allowed to open an SRK channel (by setting channel_type accordingly).
         """
+        self.check_combinations()  # test if raises
         cflags = list_enabled_bits(self)
         # channel flags must be a SUBSET of peer_features
         for cflag in cflags:
diff --git a/electrum/lnworker.py b/electrum/lnworker.py
index 68127c1..a5be386 100644
--- a/electrum/lnworker.py
+++ b/electrum/lnworker.py
@@ -1690,6 +1690,7 @@ class LNWallet(Logger):
         upfront_shutdown_script = b''
 
         assert channel_type is not None
+        channel_type.check_combinations()  # test if raises
         if channel_type & ChannelType.OPTION_ANCHORS:  # anchors
             static_payment_key = self.static_payment_key
             static_remotekey = None
diff --git a/tests/test_lnutil.py b/tests/test_lnutil.py
index cbb53e6..1bcccd1 100644
--- a/tests/test_lnutil.py
+++ b/tests/test_lnutil.py
@@ -1089,11 +1089,6 @@ class TestLNUtil(ElectrumTestCase):
         ctype = ChannelType.OPTION_STATIC_REMOTEKEY | ChannelType.OPTION_ANCHORS
         self.assertTrue(ctype.complies_with_features(pfeatures))
 
-    def test_channel_type__ignore_unknown(self):
-        # ignore unknown channel types
-        channel_type = ChannelType(0b10000000001000000000010).discard_unknown_and_check()
-        self.assertEqual(ChannelType(0b10000000001000000000000), channel_type)
-
     @as_testnet
     async def test_decode_imported_channel_backup_v0(self):
         encrypted_cb = "channel_backup:Adn87xcGIs9H2kfp4VpsOaNKWCHX08wBoqq37l1cLYKGlJamTeoaLEwpJA81l1BXF3GP/mRxqkY+whZG9l51G8izIY/kmMSvnh0DOiZEdwaaT/1/MwEHfsEomruFqs+iW24SFJPHbMM7f80bDtIxcLfZkKmgcKBAOlcqtq+dL3U3yH74S8BDDe2L4snaxxpCjF0JjDMBx1UR/28D+QlIi+lbvv1JMaCGXf+AF1+3jLQf8+lVI+rvFdyArws6Ocsvjf+ANQeSGUwW6Nb2xICQcMRgr1DO7bO4pgGu408eYRr2v3ayJBVtnKwSwd49gF5SDSjTDAO4CCM0uj9H5RxyzH7fqotkd9J80MBr84RiBXAeXKz+Ap8608/FVqgQ9BOcn6LhuAQdE5zXpmbQyw5jUGkPvHuseR+rzthzncy01odUceqTNg=="