`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.
{
    CBlockIndex* tip = m_chain.Tip();
    return strprintf("Chainstate [%s] @ height %d (%s)",
        m_from_snapshot_blockhash.IsNull() ? "ibd" : "snapshot",
        tip ? tip->nHeight : -1, tip ? tip->GetBlockHash().ToString() : "null");
}
bool CChainState::ResizeCoinsCaches(size_t coinstip_size, size_t coinsdb_size)