`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.
#else
    int fd_max = FD_SETSIZE;
#endif
    nMaxConnections = std::max(std::min<int>(nMaxConnections, fd_max - nBind - MIN_CORE_FILEDESCRIPTORS - MAX_ADDNODE_CONNECTIONS - NUM_FDS_MESSAGE_CAPTURE), 0);
    if (nFD < MIN_CORE_FILEDESCRIPTORS)
        return InitError(_("Not enough file descriptors available."));
    nMaxConnections = std::min(nFD - MIN_CORE_FILEDESCRIPTORS - MAX_ADDNODE_CONNECTIONS - NUM_FDS_MESSAGE_CAPTURE, nMaxConnections);
    if (nMaxConnections < nUserMaxConnections)
        InitWarning(strprintf(_("Reducing -maxconnections from %d to %d, because of system limitations."), nUserMaxConnections, nMaxConnections));
    
    init::SetLoggingCategories(args);
    fCheckBlockIndex = args.GetBoolArg("-checkblockindex", chainparams.DefaultConsistencyChecks());
    fCheckpointsEnabled = args.GetBoolArg("-checkpoints", DEFAULT_CHECKPOINTS_ENABLED);
    hashAssumeValid = uint256S(args.GetArg("-assumevalid", chainparams.GetConsensus().defaultAssumeValid.GetHex()));
    if (!hashAssumeValid.IsNull())
        LogPrintf("Assuming ancestors of block %s have valid signatures.\n", hashAssumeValid.GetHex());
    else
        LogPrintf("Validating signatures for all blocks.\n");
    if (args.IsArgSet("-minimumchainwork")) {
        const std::string minChainWorkStr = args.GetArg("-minimumchainwork", "");
        if (!IsHexNumber(minChainWorkStr)) {
            return InitError(strprintf(Untranslated("Invalid non-hex (%s) minimum chain work value specified"), minChainWorkStr));
        }
        nMinimumChainWork = UintToArith256(uint256S(minChainWorkStr));
    } else {
        nMinimumChainWork = UintToArith256(chainparams.GetConsensus().nMinimumChainWork);
    }
    LogPrintf("Setting nMinimumChainWork=%s\n", nMinimumChainWork.GetHex());
    if (nMinimumChainWork < UintToArith256(chainparams.GetConsensus().nMinimumChainWork)) {
        LogPrintf("Warning: nMinimumChainWork set below default value of %s\n", chainparams.GetConsensus().nMinimumChainWork.GetHex());