`banlist.dat` was introduced in https://github.com/bitcoin/bitcoin/pull/6310, storing nodes that were automatically banned (due to exceeding the misbehavior threshold) and manually banned (through the `setban` RPC).

Automatic bans were removed in https://github.com/bitcoin/bitcoin/pull/19219 and replaced with a discouragement filter. That filter is not saved to disk/persisted over shutdown/startup. The `banlist.dat` therefore now only contains addresses that have been banned through the `setban` rpc.

Since https://github.com/bitcoin/bitcoin/pull/15935, we have a specific file for configuration that is updated through the RPC and persisted over shutdown/startup, namely `settings.json`. We should therefore move the manual ban configuration from `banlist.dat` to `settings.json`. Doing so has a couple of benefits:

- `settings.json` is human readable and easily analyzable by any json parser.
- we wouldn't need to maintain custom [de]serialization code for the `banlist.dat` file.

`banlist.dat` is expected to be fairly small and infrequently updated, so disk space/performance are not huge concerns.
r
     A
    if (ShutdownRequested()) {
        LogPrintf("Shutdown requested. Exiting.\n");
        return false;
    }
     *
    if (args.GetBoolArg("-txindex", DEFAULT_TXINDEX)) {
        g_txindex = std::make_unique<TxIndex>(nTxIndexCache, false, fReindex);
        if (!g_txindex->Start(chainman.ActiveChainstate())) {
            return false;
        }
    }
    for (const auto& filter_type : g_enabled_filter_types) {
        InitBlockFilterIndex(filter_type, filter_index_cache, false, fReindex);
        if (!GetBlockFilterIndex(filter_type)->Start(chainman.ActiveChainstate())) {
            return false;
        }
    }
    if (args.GetBoolArg("-coinstatsindex", DEFAULT_COINSTATSINDEX)) {
        g_coin_stats_index = std::make_unique<CoinStatsIndex>(/* c false, fReindex);
        if (!g_coin_stats_index->Start(chainman.ActiveChainstate())) {
            return false;
        }
    }
     *
    for (const auto& client : node.chain_clients) {