`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();
    auto banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist.dat", nullptr, DEFAULT_MISBEHAVING_BANTIME);
    auto connman = std::make_unique<ConnmanTestMsg>(0x1337, 0x1337, *m_node.addrman);
    auto peerLogic = PeerManager::make(chainparams, *connman, *m_node.addrman, banman.get(),
                                       *m_node.scheduler, *m_node.chainman, *m_node.mempool, false);
    CNetAddr tor_netaddr;
    BOOST_REQUIRE(
        tor_netaddr.SetSpecial("pg6mmjiyjmcrsslvykfwnntlaru7p5svn6y2ymmju6nubxndf4pscryd.onion"));
    const CService tor_service{tor_netaddr, Params().GetDefaultPort()};
    const std::array<CAddress, 3> addr{CAddress{ip(0xa0b0c001), NODE_NONE},
                                       CAddress{ip(0xa0b0c002), NODE_NONE},
                                       CAddress{tor_service, NODE_NONE}};
    const CNetAddr other_addr{ip(0xa0b0ff01)}; 
    std::array<CNode*, 3> nodes;
    banman->ClearBanned();
    nodes[0] = new CNode{id++, NODE_NETWORK, INVALID_SOCKET, addr[0],  0,
                          0, CAddress(),  "",
                         ConnectionType::INBOUND,  false};
    nodes[0]->SetCommonVersion(PROTOCOL_VERSION);
    peerLogic->InitializeNode(nodes[0]);
    nodes[0]->fSuccessfullyConnected = true;
    connman->AddTestNode(*nodes[0]);
    peerLogic->Misbehaving(nodes[0]->GetId(), DISCOURAGEMENT_THRESHOLD,  "");