`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.
return false; 
    }
    
    const auto& params = args.m_chainparams.GetConsensus();
    assert(std::addressof(::ChainActive()) == std::addressof(m_active_chainstate.m_chain));
    auto taproot_state = VersionBitsState(m_active_chainstate.m_chain.Tip(), params, Consensus::DEPLOYMENT_TAPROOT, versionbitscache);
    if (fRequireStandard && !AreInputsStandard(tx, m_view, taproot_state == ThresholdState::ACTIVE)) {
        return state.Invalid(TxValidationResult::TX_INPUTS_NOT_STANDARD, "bad-txns-nonstandard-inputs");
    }
    
    if (tx.HasWitness() && fRequireStandard && !IsWitnessStandard(tx, m_view))
        return state.Invalid(TxValidationResult::TX_WITNESS_MUTATED, "bad-witness-nonstandard");
    int64_t nSigOpsCost = GetTransactionSigOpCost(tx, m_view, STANDARD_SCRIPT_VERIFY_FLAGS);
    
    nModifiedFees = ws.m_base_fees;
    m_pool.ApplyDelta(hash, nModifiedFees);
    
    
    bool fSpendsCoinbase = false;
    for (const CTxIn &txin : tx.vin) {
        const Coin &coin = m_view.AccessCoin(txin.prevout);
        if (coin.IsCoinBase()) {
            fSpendsCoinbase = true;
            break;
        }
    }
    assert(std::addressof(::ChainActive()) == std::addressof(m_active_chainstate.m_chain));
    entry.reset(new CTxMemPoolEntry(ptx, ws.m_base_fees, nAcceptTime, m_active_chainstate.m_chain.Height(),
            fSpendsCoinbase, nSigOpsCost, lp));
    unsigned int nSize = entry->GetTxSize();