`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.
{
        LOCK(cs_main);
        LogPrintf("block tree size = %u\n", chainman.BlockIndex().size());
        chain_active_height = chainman.ActiveChain().Height();
        if (tip_info) {
            tip_info->block_height = chain_active_height;
            tip_info->block_time = chainman.ActiveChain().Tip() ? chainman.ActiveChain().Tip()->GetBlockTime() : Params().GenesisBlock().GetBlockTime();
            tip_info->verification_progress = GuessVerificationProgress(Params().TxData(), chainman.ActiveChain().Tip());
        }
        if (tip_info && ::pindexBestHeader) {
            tip_info->header_height = ::pindexBestHeader->nHeight;
            tip_info->header_time = ::pindexBestHeader->GetBlockTime();
        }
    }
    LogPrintf("nBestHeight = %d\n", chain_active_height);
    if (node.peerman) node.peerman->SetBestHeight(chain_active_height);
    Discover();
     Map ports with UPnP or NAT-PMP.
    StartMapPort(args.GetBoolArg("-upnp", DEFAULT_UPNP), gArgs.GetBoolArg("-natpmp", DEFAULT_NATPMP));
    CConnman::Options connOptions;
    connOptions.nLocalServices = nLocalServices;
    connOptions.nMaxConnections = nMaxConnections;
    connOptions.m_max_outbound_full_relay = std::min(MAX_OUTBOUND_FULL_RELAY_CONNECTIONS, connOptions.nMaxConnections);
    connOptions.m_max_outbound_block_relay = std::min(MAX_BLOCK_RELAY_ONLY_CONNECTIONS, connOptions.nMaxConnections-connOptions.m_max_outbound_full_relay);
    connOptions.nMaxAddnode = MAX_ADDNODE_CONNECTIONS;
    connOptions.nMaxFeeler = MAX_FEELER_CONNECTIONS;