`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.
{
    const ArgsManager& args = *Assert(node.args);
    const CChainParams& chainparams = Params();
    
    if (!CreatePidFile(args)) {
        
        return false;
    }
    if (!init::StartLogging(args)) {
        
        return false;
    }
    LogPrintf("Using at most %i automatic connections (%i file descriptors available)\n", nMaxConnections, nFD);
    
    if (args.IsArgSet("-datadir") && !fs::path(args.GetArg("-datadir", "")).is_absolute()) {
        LogPrintf("Warning: relative datadir option '%s' specified, which will be interpreted relative to the " 
                  "current working directory '%s'. This is fragile, because if bitcoin is started in the future "
                  "from a different location, it will be unable to locate the current data files. There could "
                  "also be data loss if bitcoin is started while in a temporary directory.\n",
                  args.GetArg("-datadir", ""), fs::current_path().string());
    }
    InitSignatureCache();
    InitScriptExecutionCache();
    int script_threads = args.GetArg("-par", DEFAULT_SCRIPTCHECK_THREADS);
    if (script_threads <= 0) {