message: refactor: CTxMemPool::GetTotalTxSize() requires CTxMemPool::cs lock
  No change in behavior, the lock is already held at call sites.
diff: @@ -689,9 +689,9 @@ public:
  return mapTx.size();
  }
  - uint64_t GetTotalTxSize() const
  + uint64_t GetTotalTxSize() const EXCLUSIVE_LOCKS_REQUIRED(cs)
  {
  - LOCK(cs);
  + AssertLockHeld(cs);
  return totalTxSize;
  }
  