### 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

},
                    {"replaceable", RPCArg::Type::BOOL,  "wallet default", "Allow this transaction to be replaced by a transaction with higher fees via BIP 125"},
                    {"conf_target", RPCArg::Type::NUM,  "wallet default", "Confirmation target (in blocks)"},
                    {"estimate_mode", RPCArg::Type::STR,  "UNSET", "The fee estimate mode, must be one of:\n"
            "       \"UNSET\"\n"
            "       \"ECONOMICAL\"\n"
            "       \"CONSERVATIVE\""},
                },
                 RPCResult{
            "\"txid\"                   (string) The transaction id for the send. Only 1 transaction is created regardless of \n"
            "                                    the number of addresses.\n"
                 },
                RPCExamples{
            "\nSend two amounts to two different addresses:\n"
            + HelpExampleCli("sendmany", "\"\" \"{\\\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\\\":0.01,\\\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\\\":0.02}\"") +
            "\nSend two amounts to two different addresses setting the confirmation and comment:\n"
            + HelpExampleCli("sendmany", "\"\" \"{\\\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\\\":0.01,\\\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\\\":0.02}\" 6 \"testing\"") +
            "\nSend two amounts to two different addresses, subtract fee from amount:\n"
            + HelpExampleCli("sendmany", "\"\" \"{\\\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\\\":0.01,\\\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\\\":0.02}\" 1 \"\" \"[\\\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\\\",\\\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\\\"]\"") +
            "\nAs a JSON-RPC call\n"
            + HelpExampleRpc("sendmany", "\"\", {\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\":0.01,\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\":0.02}, 6, \"testing\"")
                },
    }.Check(request);
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    auto locked_chain = pwallet->chain().lock();
    LOCK(pwallet->cs_wallet);
    if (!request.params[0].isNull() && !request.params[0].get_str().empty()) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Dummy value must be set to \"\"");