message: [mempool] remove now-unnecessary code
  Remove variables used for keeping track of mempool transactions for
  which we haven't processed the parents yet. Since we're iterating in
  topological order now, they're always unused.
diff: @@ -685,15 +685,12 @@ void CTxMemPool::check(CChainState& active_chainstate) const
  CCoinsViewCache mempoolDuplicate(const_cast<CCoinsViewCache*>(&active_coins_tip));
  const int64_t spendheight = active_chainstate.m_chain.Height() + 1;
  - std::list<const CTxMemPoolEntry*> waitingOnDependants;
  for (const auto& it : GetSortedDepthAndScore()) {
  - unsigned int i = 0;
  checkTotal += it->GetTxSize();
  check_total_fee += it->GetFee();
  innerUsage += it->DynamicMemoryUsage();
  const CTransaction& tx = it->GetTx();
  innerUsage += memusage::DynamicUsage(it->GetMemPoolParentsConst()) + memusage::DynamicUsage(it->GetMemPoolChildrenConst());
  - bool fDependsWait = false;
  CTxMemPoolEntry::Parents setParentCheck;
  for (const CTxIn &txin : tx.vin) {
  // Check that every mempool transaction's inputs refer to available coins, or other mempool tx's.
  @@ -701,7 +698,10 @@ void CTxMemPool::check(CChainState& active_chainstate) const
  if (it2 != mapTx.end()) {
  const CTransaction& tx2 = it2->GetTx();
  assert(tx2.vout.size() > txin.prevout.n && !tx2.vout[txin.prevout.n].IsNull());
  - if (!mempoolDuplicate.HaveCoin(txin.prevout)) fDependsWait = true;
  + // We are iterating through the mempool entries sorted in order by ancestor count.
  + // All parents must have been checked before their children and their coins added to
  + // the mempoolDuplicate coins cache.
  + assert(mempoolDuplicate.HaveCoin(txin.prevout));
  setParentCheck.insert(*it2);
  } else {
  assert(active_coins_tip.HaveCoin(txin.prevout));
  @@ -711,7 +711,6 @@ void CTxMemPool::check(CChainState& active_chainstate) const
  assert(it3 != mapNextTx.end());
  assert(it3->first == &txin.prevout);
  assert(it3->second == &tx);
  - i++;
  }
  auto comp = [](const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) -> bool {
  return a.GetTx().GetHash() == b.GetTx().GetHash();
  @@ -759,25 +758,8 @@ void CTxMemPool::check(CChainState& active_chainstate) const
  // just a sanity check, not definitive that this calc is correct...
  assert(it->GetSizeWithDescendants() >= child_sizes + it->GetTxSize());
  - if (fDependsWait)
  - waitingOnDependants.push_back(&(*it));
  - else {
  CheckInputsAndUpdateCoins(tx, mempoolDuplicate, spendheight);
  }
  - }
  - unsigned int stepsSinceLastRemove = 0;
  - while (!waitingOnDependants.empty()) {
  - const CTxMemPoolEntry* entry = waitingOnDependants.front();
  - waitingOnDependants.pop_front();
  - if (!mempoolDuplicate.HaveInputs(entry->GetTx())) {
  - waitingOnDependants.push_back(entry);
  - stepsSinceLastRemove++;
  - assert(stepsSinceLastRemove < waitingOnDependants.size());
  - } else {
  - CheckInputsAndUpdateCoins(entry->GetTx(), mempoolDuplicate, spendheight);
  - stepsSinceLastRemove = 0;
  - }
  - }
  for (auto it = mapNextTx.cbegin(); it != mapNextTx.cend(); it++) {
  uint256 hash = it->second->GetHash();
  indexed_transaction_set::const_iterator it2 = mapTx.find(hash);
  