`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.
{
    
    try {
        CHashWriter hasher(stream.GetType(), stream.GetVersion());
        stream << Params().MessageStart() << data;
        hasher << Params().MessageStart() << data;
        stream << hasher.GetHash();
    } catch (const std::exception& e) {
        return error("%s: Serialize or I/O error - %s", __func__, e.what());
    }
    return true;
}
template <typename Data>
bool SerializeFileDB(const std::string& prefix, const fs::path& path, const Data& data, int version)
{
    
    uint16_t randv = 0;
    GetRandBytes((unsigned char*)&randv, sizeof(randv));
    std::string tmpfn = strprintf("%s.%04x", prefix, randv);