validation: remove nchaintx from assumeutxo metadata

This value is no longer used and is instead specified statically
in chainparams. This change means that previously generated
snapshots will no longer be usable.

src/node/utxo_snapshot.h

@@ -22,22 +22,15 @@ class SnapshotMetadata
     //! during snapshot load to estimate progress of UTXO set reconstruction.
     uint64_t m_coins_count = 0;
 
-    //! Necessary to "fake" the base nChainTx so that we can estimate progress during
-    //! initial block download for the assumeutxo chainstate.
-    //!
-    //! TODO: this is unused and should be removed.
-    unsigned int m_nchaintx = 0;
-
     SnapshotMetadata() { }
     SnapshotMetadata(
         const uint256& base_blockhash,
         uint64_t coins_count,
         unsigned int nchaintx) :
             m_base_blockhash(base_blockhash),
-            m_coins_count(coins_count),
-            m_nchaintx(nchaintx) { }
+            m_coins_count(coins_count) { }
 
-    SERIALIZE_METHODS(SnapshotMetadata, obj) { READWRITE(obj.m_base_blockhash, obj.m_coins_count, obj.m_nchaintx); }
+    SERIALIZE_METHODS(SnapshotMetadata, obj) { READWRITE(obj.m_base_blockhash, obj.m_coins_count); }
 };
 
 #endif // BITCOIN_NODE_UTXO_SNAPSHOT_H

src/test/validation_chainstatemanager_tests.cpp

@@ -266,16 +266,7 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
             metadata.m_base_blockhash = uint256::ONE;
     }));
 
-    constexpr int bad_nchaintx = 9999;
-
-    BOOST_REQUIRE(CreateAndActivateUTXOSnapshot(
-        m_node, m_path_root, [](CAutoFile& auto_infile, SnapshotMetadata& metadata) {
-            // Provide an nChainTx that differs from the hardcoded one.
-            //
-            // Ultimately this malleation check should be removed when we remove
-            // the now-unnecessary nChainTx from the user-specified snapshot metadata.
-            metadata.m_nchaintx = bad_nchaintx;
-    }));
+    BOOST_REQUIRE(CreateAndActivateUTXOSnapshot(m_node, m_path_root));
 
     // Ensure our active chain is the snapshot chainstate.
     BOOST_CHECK(!chainman.ActiveChainstate().m_from_snapshot_blockhash.IsNull());
@@ -286,10 +277,7 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
     const AssumeutxoData& au_data = *ExpectedAssumeutxo(snapshot_height, ::Params());
     const CBlockIndex* tip = chainman.ActiveTip();
 
-    // Ensure that, despite a bad nChainTx value being in the snapshot, activation
-    // uses the hardcoded value from chainparams.
     BOOST_CHECK_EQUAL(tip->nChainTx, au_data.nChainTx);
-    BOOST_CHECK(tip->nChainTx != bad_nchaintx);
 
     // To be checked against later when we try loading a subsequent snapshot.
     uint256 loaded_snapshot_blockhash{*chainman.SnapshotBlockhash()};