message: [refactor] put finality and maturity checking into a lambda
  No behavior change.
diff: @@ -631,8 +631,13 @@ void CTxMemPool::removeForReorg(CChainState& active_chainstate, int flags)
  {
  // Remove transactions spending a coinbase which are now immature and no-longer-final transactions
  AssertLockHeld(cs);
  - setEntries txToRemove;
  - for (indexed_transaction_set::const_iterator it = mapTx.begin(); it != mapTx.end(); it++) {
  + AssertLockHeld(::cs_main);
  +
  + const auto check_final_and_mature = [this, &active_chainstate, flags](txiter it)
  + EXCLUSIVE_LOCKS_REQUIRED(cs, ::cs_main) {
  + bool should_remove = false;
  + AssertLockHeld(cs);
  + AssertLockHeld(::cs_main);
  const CTransaction& tx = it->GetTx();
  LockPoints lp = it->GetLockPoints();
  const bool validLP = TestLockPointValidity(active_chainstate.m_chain, &lp);
  @@ -641,7 +646,7 @@ void CTxMemPool::removeForReorg(CChainState& active_chainstate, int flags)
  || !CheckSequenceLocks(active_chainstate.m_chain.Tip(), view_mempool, tx, flags, &lp, validLP)) {
  // Note if CheckSequenceLocks fails the LockPoints may still be invalid
  // So it's critical that we remove the tx and not depend on the LockPoints.
  - txToRemove.insert(it);
  + should_remove = true;
  } else if (it->GetSpendsCoinbase()) {
  for (const CTxIn& txin : tx.vin) {
  indexed_transaction_set::const_iterator it2 = mapTx.find(txin.prevout.hash);
  @@ -651,11 +656,17 @@ void CTxMemPool::removeForReorg(CChainState& active_chainstate, int flags)
  if (m_check_ratio != 0) assert(!coin.IsSpent());
  unsigned int nMemPoolHeight = active_chainstate.m_chain.Tip()->nHeight + 1;
  if (coin.IsSpent() || (coin.IsCoinBase() && ((signed long)nMemPoolHeight) - coin.nHeight < Params().GetConsensus().nCoinbaseMaturity)) {
  - txToRemove.insert(it);
  + should_remove = true;
  break;
  }
  }
  }
  + return should_remove;
  + };
  +
  + setEntries txToRemove;
  + for (indexed_transaction_set::const_iterator it = mapTx.begin(); it != mapTx.end(); it++) {
  + if (check_final_and_mature(it)) txToRemove.insert(it);
  }
  setEntries setAllRemoves;
  for (txiter it : txToRemove) {
  