`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 CTransaction& tx = *ws.m_ptx;
    const uint256& hash = ws.m_hash;
    TxValidationState& state = ws.m_state;
    const bool bypass_limits = args.m_bypass_limits;
    CTxMemPool::setEntries& allConflicting = ws.m_all_conflicting;
    CTxMemPool::setEntries& setAncestors = ws.m_ancestors;
    const CAmount& nModifiedFees = ws.m_modified_fees;
    const CAmount& nConflictingFees = ws.m_conflicting_fees;
    const size_t& nConflictingSize = ws.m_conflicting_size;
    const bool fReplacementTransaction = ws.m_replacement_transaction;
    std::unique_ptr<CTxMemPoolEntry>& entry = ws.m_entry;