`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.
if (pa->nChainWork > pb->nChainWork) return false;
    if (pa->nChainWork < pb->nChainWork) return true;
    
    if (pa->nSequenceId < pb->nSequenceId) return false;
    if (pa->nSequenceId > pb->nSequenceId) return true;
    
    
    if (pa < pb) return false;
    if (pa > pb) return true;
    
    return false;
}
ChainstateManager g_chainman;
CChainState& ChainstateActive()
{
    LOCK(::cs_main);
    assert(g_chainman.m_active_chainstate);
    return *g_chainman.m_active_chainstate;
}
CChain& ChainActive()