`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.
options.m_msgproc = m_node.peerman.get();
        m_node.connman->Init(options);
    }
}
TestChain100Setup::TestChain100Setup()
{
    SetMockTime(1598887952);
    constexpr std::array<unsigned char, 32> vchKey = {
        {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}};
    coinbaseKey.Set(vchKey.begin(), vchKey.end(), true);
    
    this->mineBlocks(COINBASE_MATURITY);
    {
        LOCK(::cs_main);
        assert(
            m_node.chainman->ActiveChain().Tip()->GetBlockHash().ToString() ==
            "571d80a9967ae599cec0448b0b0ba1cfb606f584d8069bd7166b86854ba7a191");
    }
}
void TestChain100Setup::mineBlocks(int num_blocks)
{
    CScript scriptPubKey = CScript() << ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;
    for (int i = 0; i < num_blocks; i++) {
        std::vector<CMutableTransaction> noTxns;
        CBlock b = CreateAndProcessBlock(noTxns, scriptPubKey);
        SetMockTime(GetTime() + 1);
        m_coinbase_txns.push_back(b.vtx[0]);
    }
}
CBlock TestChain100Setup::CreateAndProcessBlock(const std::vector<CMutableTransaction>& txns, const CScript& scriptPubKey)