Fix compilation for old Boost versions

diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index e63bff2a..49961896 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -988,7 +988,7 @@ util::Result<std::pair<std::vector<FeeFrac>, std::vector<FeeFrac>>> CTxMemPool::
 CTxMemPool::ChangeSet::TxHandle CTxMemPool::ChangeSet::StageAddition(const CTransactionRef& tx, const CAmount fee, int64_t time, unsigned int entry_height, uint64_t entry_sequence, bool spends_coinbase, int64_t sigops_cost, LockPoints lp)
 {
     LOCK(m_pool->cs);
-    Assume(!m_to_add.contains(tx->GetHash()));
+    Assume(m_to_add.find(tx->GetHash()) == m_to_add.end());
     Assume(!m_dependencies_processed);
 
     // We need to process dependencies after adding a new transaction.
diff --git a/src/txrequest.cpp b/src/txrequest.cpp
index bb013b0f..4d7240be 100644
--- a/src/txrequest.cpp
+++ b/src/txrequest.cpp
@@ -580,7 +580,7 @@ public:
         // Bail out if we already have a CANDIDATE_BEST announcement for this (txhash, peer) combination. The case
         // where there is a non-CANDIDATE_BEST announcement already will be caught by the uniqueness property of the
         // ByPeer index when we try to emplace the new object below.
-        if (m_index.get<ByPeer>().contains(ByPeerView{peer, true, gtxid.ToUint256()})) return;
+        if (m_index.get<ByPeer>().count(ByPeerView{peer, true, gtxid.ToUint256()})) return;
 
         // Try creating the announcement with CANDIDATE_DELAYED state (which will fail due to the uniqueness
         // of the ByPeer index if a non-CANDIDATE_BEST announcement already exists with the same txhash and peer).