### 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

{
            RPCHelpMan{"listwallets",
                "Returns a list of currently loaded wallets.\n"
                "For full information on the wallet, use \"getwalletinfo\"\n",
                {},
                RPCResult{
            "[                         (json array of strings)\n"
            "  \"walletname\"            (string) the wallet name\n"
            "   ...\n"
            "]\n"
                },
                RPCExamples{
                    HelpExampleCli("listwallets", "")
            + HelpExampleRpc("listwallets", "")
                },
            }.Check(request);
    UniValue obj(UniValue::VARR);
    for (const std::shared_ptr<CWallet>& wallet : GetWallets()) {
        if (!EnsureWalletIsAvailable(wallet.get(), request.fHelp)) {
            return NullUniValue;
        }
        LOCK(wallet->cs_wallet);
        obj.push_back(wallet->GetName());
    }
    return obj;
}
static UniValue loadwallet(const JSONRPCRequest& request)