`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.
{
    const std::string URL_SOURCE_CODE = "<https:github.com/bitcoin/bitcoin>";
    return CopyrightHolders(strprintf(_("Copyright (C) %i-%i").translated, 2009, COPYRIGHT_YEAR) + " ") + "\n" +
           "\n" +
           strprintf(_("Please contribute if you find %s useful. "
                       "Visit %s for further information about the software.").translated,
               PACKAGE_NAME, "<" PACKAGE_URL ">") +
           "\n" +
           strprintf(_("The source code is available from %s.").translated,
               URL_SOURCE_CODE) +
           "\n" +
           "\n" +
           _("This is experimental software.").translated + "\n" +
           strprintf(_("Distributed under the MIT software license, see the accompanying file %s or %s").translated, "COPYING", "<https:opensource.org/licenses/MIT>") +
           "\n";
}
static bool fHaveGenesis = false;
static Mutex g_genesis_wait_mutex;
static std::condition_variable g_genesis_wait_cv;
static void BlockNotifyGenesisWait(const CBlockIndex* pBlockIndex)
{
    if (pBlockIndex != nullptr) {
        {
            LOCK(g_genesis_wait_mutex);
            fHaveGenesis = true;
        }
        g_genesis_wait_cv.notify_all();
    }
}
static void CleanupBlockRevFiles()