`RewindBlockIndex` was made to allow nodes upgrading to new consensus rules post-segwit fork to 
download new consensus data (i.e witnesses) without having to go through a whole IBD. It has been pointed than now really few pre-segwit nodes care to upgrade and that this logic may be irrelevant.

See https://github.com/bitcoin/bitcoin/pull/17737#discussion_r358514335 in review  of #17737 for more context pointers.
bool fReplacementOptOut = true;
                for (const CTxIn &_txin : ptxConflicting->vin)
                {
                    if (_txin.nSequence <= MAX_BIP125_RBF_SEQUENCE)
                    {
                        fReplacementOptOut = false;
                        break;
                    }
                }
                if (fReplacementOptOut) {
                    return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "txn-mempool-conflict");
                }
                setConflicts.insert(ptxConflicting->GetHash());
            }
        }
    }
    LockPoints lp;
    m_view.SetBackend(m_viewmempool);
    assert(std::addressof(::ChainstateActive().CoinsTip()) == std::addressof(m_active_chainstate.CoinsTip()));
    const CCoinsViewCache& coins_cache = m_active_chainstate.CoinsTip();
    
    for (const CTxIn& txin : tx.vin) {
        if (!coins_cache.HaveCoinInCache(txin.prevout)) {
            coins_to_uncache.push_back(txin.prevout);
        }