`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.
{
    AssertLockHeld(cs_main);
    AssertLockHeld(m_mempool.cs);
    assert(std::addressof(::ChainstateActive()) == std::addressof(*this));
    const CBlockIndex* pindexOldTip = m_chain.Tip();
    const CBlockIndex* pindexFork = m_chain.FindFork(pindexMostWork);
    
    bool fBlocksDisconnected = false;
    DisconnectedBlockTransactions disconnectpool;
    while (m_chain.Tip() && m_chain.Tip() != pindexFork) {
        if (!DisconnectTip(state, chainparams, &disconnectpool)) {
            
            
            UpdateMempoolForReorg(*this, m_mempool, disconnectpool, false);