`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.
{
    LOCK2(cs_main, cs_LastBlockFile);
    if (chain_tip_height < 0 || nPruneTarget == 0) {
        return;
    }
    if ((uint64_t)chain_tip_height <= nPruneAfterHeight) {
        return;
    }
    unsigned int nLastBlockWeCanPrune = std::min(prune_height, chain_tip_height - static_cast<int>(MIN_BLOCKS_TO_KEEP));
    uint64_t nCurrentUsage = CalculateCurrentUsage();
    
    
    
    uint64_t nBuffer = BLOCKFILE_CHUNK_SIZE + UNDOFILE_CHUNK_SIZE;
    uint64_t nBytesToPrune;
    int count = 0;
    if (nCurrentUsage + nBuffer >= nPruneTarget) {
        
        
        
        
        if (is_ibd) {
            
            nBuffer += nPruneTarget / 10;