`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.
{
    const CChainParams& chainparams = Params();
    CTxMemPool empty_pool;
    CBlock block = BlockAssembler(m_node.chainman->ActiveChainstate(), empty_pool, chainparams).CreateNewBlock(scriptPubKey)->block;
    Assert(block.vtx.size() == 1);
    for (const CMutableTransaction& tx : txns) {
        block.vtx.push_back(MakeTransactionRef(tx));
    }
    RegenerateCommitments(block, *Assert(m_node.chainman));
    while (!CheckProofOfWork(block.GetHash(), block.nBits, chainparams.GetConsensus())) ++block.nNonce;
    std::shared_ptr<const CBlock> shared_pblock = std::make_shared<const CBlock>(block);
    Assert(m_node.chainman)->ProcessNewBlock(chainparams, shared_pblock, true, nullptr);
    return block;
}
CMutableTransaction TestChain100Setup::CreateValidMempoolTransaction(CTransactionRef input_transaction,
                                                                     int input_vout,
                                                                     int input_height,
                                                                     CKey input_signing_key,
                                                                     CScript output_destination,
                                                                     CAmount output_amount,
                                                                     bool submit)
{
    
    CMutableTransaction mempool_txn;
    
    COutPoint outpoint_to_spend(input_transaction->GetHash(), input_vout);
    CTxIn input(outpoint_to_spend);
    mempool_txn.vin.push_back(input);