`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.
{
    {
        LOCK(cs_main);
        if (pindex->nChainWork < m_chain.Tip()->nChainWork) {
            
            return true;
        }
        if (m_chain.Tip()->nChainWork > nLastPreciousChainwork) {
            
            nBlockReverseSequenceId = -1;
        }
        nLastPreciousChainwork = m_chain.Tip()->nChainWork;
        setBlockIndexCandidates.erase(pindex);
        pindex->nSequenceId = nBlockReverseSequenceId;
        if (nBlockReverseSequenceId > std::numeric_limits<int32_t>::min()) {
            
            
            nBlockReverseSequenceId--;
        }
        if (pindex->IsValid(BLOCK_VALID_TRANSACTIONS) && pindex->HaveTxsDownloaded()) {
            setBlockIndexCandidates.insert(pindex);
            PruneBlockIndexCandidates();
        }
    }
    return ActivateBestChain(state, params, std::shared_ptr<const CBlock>());
}
bool CChainState::InvalidateBlock(BlockValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex)
{
    
    assert(pindex);