`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.
tx.vin[0].prevout.n = 0;
        tx.vin[0].prevout.hash = InsecureRand256();
        tx.vin[0].scriptSig << OP_1;
        tx.vout.resize(1);
        tx.vout[0].nValue = 1*CENT;
        tx.vout[0].scriptPubKey = GetScriptForDestination(PKHash(key.GetPubKey()));
        orphanage.AddTx(MakeTransactionRef(tx), i);
    }
    
    for (int i = 0; i < 50; i++)
    {
        CTransactionRef txPrev = orphanage.RandomOrphan();
        CMutableTransaction tx;
        tx.vin.resize(1);
        tx.vin[0].prevout.n = 0;
        tx.vin[0].prevout.hash = txPrev->GetHash();
        tx.vout.resize(1);
        tx.vout[0].nValue = 1*CENT;
        tx.vout[0].scriptPubKey = GetScriptForDestination(PKHash(key.GetPubKey()));
        BOOST_CHECK(SignSignature(keystore, *txPrev, tx, 0, SIGHASH_ALL));
        orphanage.AddTx(MakeTransactionRef(tx), i);
    }
    
    for (int i = 0; i < 10; i++)
    {
        CTransactionRef txPrev = orphanage.RandomOrphan();
        CMutableTransaction tx;
        tx.vout.resize(1);
        tx.vout[0].nValue = 1*CENT;
        tx.vout[0].scriptPubKey = GetScriptForDestination(PKHash(key.GetPubKey()));