`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.
{
    static Mutex g_shutdown_mutex;
    TRY_LOCK(g_shutdown_mutex, lock_shutdown);
    if (!lock_shutdown) return;
    LogPrintf("%s: In progress...\n", __func__);
    Assert(node.args);
    
    
    
    
    util::ThreadRename("shutoff");
    if (node.mempool) node.mempool->AddTransactionsUpdated(1);
    StopHTTPRPC();
    StopREST();
    StopRPC();
    StopHTTPServer();
    for (const auto& client : node.chain_clients) {
        client->flush();
    }
    StopMapPort();
    
    
    if (node.peerman) UnregisterValidationInterface(node.peerman.get());
    if (node.connman) node.connman->Stop();
    StopTorControl();
    
    
    if (node.scheduler) node.scheduler->stop();