`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.
{
    AssertLockHeld(cs_main);
    LOCK(m_pool.cs); 
    Workspace ws(ptx);
    if (!PreChecks(args, ws)) return MempoolAcceptResult(ws.m_state);
    
    
    
    
    PrecomputedTransactionData txdata;
    if (!PolicyScriptChecks(args, ws, txdata)) return MempoolAcceptResult(ws.m_state);
    if (!ConsensusScriptChecks(args, ws, txdata)) return MempoolAcceptResult(ws.m_state);
    
    if (args.m_test_accept) {
        return MempoolAcceptResult(std::move(ws.m_replaced_transactions), ws.m_base_fees);
    }
    if (!Finalize(args, ws)) return MempoolAcceptResult(ws.m_state);
    GetMainSignals().TransactionAddedToMempool(ptx, m_pool.GetAndIncrementSequence());
    return MempoolAcceptResult(std::move(ws.m_replaced_transactions), ws.m_base_fees);
}
} 
static MempoolAcceptResult AcceptToMemoryPoolWithTime(const CChainParams& chainparams, CTxMemPool& pool,
                                                      CChainState& active_chainstate,
                                                      const CTransactionRef &tx, int64_t nAcceptTime,
                                                      bool bypass_limits, bool test_accept)
                                                      EXCLUSIVE_LOCKS_REQUIRED(cs_main)