`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.
const CTxMemPool& pool,
                        const CTransaction& tx,
                        int flags,
                        LockPoints* lp,
                        bool useExistingLockPoints)
{
    AssertLockHeld(cs_main);
    AssertLockHeld(pool.cs);
    assert(std::addressof(::ChainstateActive()) == std::addressof(active_chainstate));
    CBlockIndex* tip = active_chainstate.m_chain.Tip();
    assert(tip != nullptr);
    CBlockIndex index;
    index.pprev = tip;
    
    
    
    
    
    
    index.nHeight = tip->nHeight + 1;
    std::pair<int, int64_t> lockPair;
    if (useExistingLockPoints) {
        assert(lp);
        lockPair.first = lp->height;
        lockPair.second = lp->time;
    }
    else {