`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.
LogPrintf("[snapshot] Did not find snapshot start blockheader %s\n",
                  base_blockhash.ToString());
        return false;
    }
    CCoinsStats stats;
    auto breakpoint_fnc = [] {  };
    
    
    CCoinsViewDB* snapshot_coinsdb = WITH_LOCK(::cs_main, return &snapshot_chainstate.CoinsDB());
    if (!GetUTXOStats(snapshot_coinsdb, WITH_LOCK(::cs_main, return std::ref(m_blockman)), stats, CoinStatsHashType::HASH_SERIALIZED, breakpoint_fnc)) {
        LogPrintf("[snapshot] failed to generate coins stats\n");
        return false;
    }
    
    int base_height = snapshot_start_block->nHeight;
    auto maybe_au_data = ExpectedAssumeutxo(base_height, ::Params());
    if (!maybe_au_data) {
        LogPrintf("[snapshot] assumeutxo height in snapshot metadata not recognized " 
            "(%d) - refusing to load snapshot\n", base_height);
        return false;
    }
    const AssumeutxoData& au_data = *maybe_au_data;
    if (stats.hashSerialized != au_data.hash_serialized) {
        LogPrintf("[snapshot] bad snapshot content hash: expected %s, got %s\n",
            au_data.hash_serialized.ToString(), stats.hashSerialized.ToString());
        return false;
    }
    snapshot_chainstate.m_chain.SetTip(snapshot_start_block);