`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.
{
    fsbridge::ofstream file{GetPidFile(args)};
    if (file) {
#ifdef WIN32
        tfm::format(file, "%d\n", GetCurrentProcessId());
#else
        tfm::format(file, "%d\n", getpid());
#endif
        return true;
    } else {
        return InitError(strprintf(_("Unable to create the PID file '%s': %s"), GetPidFile(args).string(), std::strerror(errno)));
    }
}
void Interrupt(NodeContext& node)
{
    InterruptHTTPServer();
    InterruptHTTPRPC();
    InterruptRPC();
    InterruptREST();
    InterruptTorControl();
    InterruptMapPort();
    if (node.connman)
        node.connman->Interrupt();
    if (g_txindex) {
        g_txindex->Interrupt();
    }
    ForEachBlockFilterIndex([](BlockFilterIndex& index) { index.Interrupt(); });
}
void Shutdown(NodeContext& node)