`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.
{
    static Mutex g_shutdown_mutex;
    TRY_LOCK(g_shutdown_mutex, lock_shutdown);
    if (!lock_shutdown) return;
    LogPrintf("%s: In progress...\n", __func__);
    Assert(node.args);
    
    
    
    
    util::ThreadRename("shutoff");
    if (node.mempool) node.mempool->AddTransactionsUpdated(1);
    StopHTTPRPC();
    StopREST();
    StopRPC();
    StopHTTPServer();
    for (const auto& client : node.chain_clients) {
        client->flush();
    }
    StopMapPort();
    
    
    if (node.peerman) UnregisterValidationInterface(node.peerman.get());
    if (node.connman) node.connman->Stop();