`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.
if (args.SoftSetBoolArg("-upnp", false))
            LogPrintf("%s: parameter interaction: -proxy set -> setting -upnp=0\n", __func__);
        if (args.SoftSetBoolArg("-natpmp", false)) {
            LogPrintf("%s: parameter interaction: -proxy set -> setting -natpmp=0\n", __func__);
        }
        
        if (args.SoftSetBoolArg("-discover", false))
            LogPrintf("%s: parameter interaction: -proxy set -> setting -discover=0\n", __func__);
    }
    if (!args.GetBoolArg("-listen", DEFAULT_LISTEN)) {
        
        if (args.SoftSetBoolArg("-upnp", false))
            LogPrintf("%s: parameter interaction: -listen=0 -> setting -upnp=0\n", __func__);
        if (args.SoftSetBoolArg("-natpmp", false)) {
            LogPrintf("%s: parameter interaction: -listen=0 -> setting -natpmp=0\n", __func__);
        }
        if (args.SoftSetBoolArg("-discover", false))
            LogPrintf("%s: parameter interaction: -listen=0 -> setting -discover=0\n", __func__);
        if (args.SoftSetBoolArg("-listenonion", false))
            LogPrintf("%s: parameter interaction: -listen=0 -> setting -listenonion=0\n", __func__);
        if (args.SoftSetBoolArg("-i2pacceptincoming", false)) {
            LogPrintf("%s: parameter interaction: -listen=0 -> setting -i2pacceptincoming=0\n", __func__);
        }
    }
    if (args.IsArgSet("-externalip")) {
        
        if (args.SoftSetBoolArg("-discover", false))
            LogPrintf("%s: parameter interaction: -externalip set -> setting -discover=0\n", __func__);
    }