`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.
}
    nConnectTimeout = args.GetArg("-timeout", DEFAULT_CONNECT_TIMEOUT);
    if (nConnectTimeout <= 0) {
        nConnectTimeout = DEFAULT_CONNECT_TIMEOUT;
    }
    peer_connect_timeout = args.GetArg("-peertimeout", DEFAULT_PEER_CONNECT_TIMEOUT);
    if (peer_connect_timeout <= 0) {
        return InitError(Untranslated("peertimeout cannot be configured with a negative value."));
    }
    if (args.IsArgSet("-minrelaytxfee")) {
        CAmount n = 0;
        if (!ParseMoney(args.GetArg("-minrelaytxfee", ""), n)) {
            return InitError(AmountErrMsg("minrelaytxfee", args.GetArg("-minrelaytxfee", "")));
        }
        
        ::minRelayTxFee = CFeeRate(n);
    } else if (incrementalRelayFee > ::minRelayTxFee) {
        
        ::minRelayTxFee = incrementalRelayFee;
        LogPrintf("Increasing minrelaytxfee to %s to match incrementalrelayfee\n",::minRelayTxFee.ToString());
    }
    
    
    if (args.IsArgSet("-blockmintxfee")) {
        CAmount n = 0;
        if (!ParseMoney(args.GetArg("-blockmintxfee", ""), n))
            return InitError(AmountErrMsg("blockmintxfee", args.GetArg("-blockmintxfee", "")));
    }