`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.
{
    return DeserializeFileDB(pathAddr, addr, CLIENT_VERSION);
}
bool CAddrDB::Read(CAddrMan& addr, CDataStream& ssPeers)
{
    bool ret = DeserializeDB(ssPeers, addr, false);
    if (!ret) {
        
        addr.Clear();
    }
    return ret;
}
void DumpAnchors(const fs::path& anchors_db_path, const std::vector<CAddress>& anchors)
{
    LOG_TIME_SECONDS(strprintf("Flush %d outbound block-relay-only peer addresses to anchors.dat", anchors.size()));
    SerializeFileDB("anchors", anchors_db_path, anchors, CLIENT_VERSION | ADDRV2_FORMAT);
}
std::vector<CAddress> ReadAnchors(const fs::path& anchors_db_path)
{
    std::vector<CAddress> anchors;
    if (DeserializeFileDB(anchors_db_path, anchors, CLIENT_VERSION | ADDRV2_FORMAT)) {
        LogPrintf("Loaded %i addresses from %s\n", anchors.size(), anchors_db_path.filename());
    } else {
        anchors.clear();
    }
    fs::remove(anchors_db_path);
    return anchors;
}