### Describe the issue

Testing in bitcoin 0.13.0, calling `bitcoin-cli listsinceblock x` is outputting all double-spent transactions that are in the wallet, even those that were double-spent well and truly before x.
### Is the issue reproducible?

Yes
#### List steps to reproduce below:
1.   Create a double-spend send to your wallet (easiest using bip125)
2.   Wait until one confirms, and then wait a few more blocks
3.   Run `bitcoin-cli listsinceblock $(bitcoin-cli getbestblockhash)` and it will output the double spent transaction
### Expected behavior

The double-spent transaction that was conflicted before the block hash should be filtered

{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
            RPCHelpMan{"listtransactions",
                "\nIf a label name is provided, this will return only incoming transactions paying to addresses with the specified label.\n"
                "\nReturns up to 'count' most recent transactions skipping the first 'from' transactions.\n",
                {
                    {"label", RPCArg::Type::STR, RPCArg::Optional::OMITTED_NAMED_ARG, "If set, should be a valid label name to return only incoming transactions\n"
            "              with the specified label, or \"*\" to disable filtering and return all transactions."},
                    {"count", RPCArg::Type::NUM,  "10", "The number of transactions to return"},
                    {"skip", RPCArg::Type::NUM,  "0", "The number of transactions to skip"},