Remove cs_main lock annotation from ChainstateManager.m_blockman

Summary:
BlockManager is a large data structure, and cs_main is not required to
take its address or access every part of it. Individual BlockManager
fields and methods which do require cs_main like m_block_index and
LookupBlockIndex are already annotated separately, and these other
annotations describe locking requirements more accurately and do a
better job enforcing thread safety.

Since cs_main is not needed to access the address of the m_block object,
this commit drops cs_main LOCK calls which were added pointlessly to
satisfy this annotation in the past.

Co-authored-by: Carl Dong <[email protected]>

This is a backport of [[bitcoin/bitcoin#24024 | core#24024]]

Test Plan:
With clang and Debug
`ninja all check-all`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12909

src/test/fuzz/coins_view.cpp

@@ -307,12 +307,9 @@ void test_one_input(const std::vector<uint8_t> &buffer) {
                 CCoinsStats stats{CoinStatsHashType::HASH_SERIALIZED};
                 bool expected_code_path = false;
                 try {
-                    (void)GetUTXOStats(
-                        &coins_view_cache,
-                        WITH_LOCK(::cs_main,
-                                  return std::ref(
-                                      g_setup->m_node.chainman->m_blockman)),
-                        stats);
+                    (void)GetUTXOStats(&coins_view_cache,
+                                       g_setup->m_node.chainman->m_blockman,
+                                       stats);
                 } catch (const std::logic_error &) {
                     expected_code_path = true;
                 }

src/validation.cpp

@@ -6037,9 +6037,7 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
     CCoinsViewDB *snapshot_coinsdb =
         WITH_LOCK(::cs_main, return &snapshot_chainstate.CoinsDB());
 
-    if (!GetUTXOStats(snapshot_coinsdb,
-                      WITH_LOCK(::cs_main, return std::ref(m_blockman)), stats,
-                      breakpoint_fnc)) {
+    if (!GetUTXOStats(snapshot_coinsdb, m_blockman, stats, breakpoint_fnc)) {
         LogPrintf("[snapshot] failed to generate coins stats\n");
         return false;
     }

src/validation.h

@@ -1148,7 +1148,7 @@ class ChainstateManager {
     std::thread m_load_block;
     //! A single BlockManager instance is shared across each constructed
     //! chainstate to avoid duplicating block metadata.
-    node::BlockManager m_blockman GUARDED_BY(::cs_main);
+    node::BlockManager m_blockman;
 
     /**
      * In order to efficiently track invalidity of headers, we keep the set of