`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.
CCoinsViewCache& view, const CChainParams& chainparams, bool fJustCheck)
{
    AssertLockHeld(cs_main);
    assert(pindex);
    assert(*pindex->phashBlock == block.GetHash());
    int64_t nTimeStart = GetTimeMicros();
    
    
    
    
    
    
    
    
    
    
    
    
    
    if (!CheckBlock(block, state, chainparams.GetConsensus(), !fJustCheck, !fJustCheck)) {
        if (state.GetResult() == BlockValidationResult::BLOCK_MUTATED) {
            
            
            
            return AbortNode(state, "Corrupt block found indicating potential hardware failure; shutting down");
        }