### 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

passphrase.reserve(100);
    std::vector<std::string> warnings;
    if (!request.params[3].isNull()) {
        passphrase = request.params[3].get_str().c_str();
        if (passphrase.empty()) {
            
            warnings.emplace_back("Empty string given as passphrase, wallet will not be encrypted.");
        }
    }
    if (!request.params[4].isNull() && request.params[4].get_bool()) {
        flags |= WALLET_FLAG_AVOID_REUSE;
    }
    std::string error;
    std::shared_ptr<CWallet> wallet;
    WalletCreationStatus status = CreateWallet(*g_rpc_interfaces->chain, passphrase, flags, request.params[0].get_str(), error, warnings, wallet);
    switch (status) {
        case WalletCreationStatus::CREATION_FAILED:
            throw JSONRPCError(RPC_WALLET_ERROR, error);
        case WalletCreationStatus::ENCRYPTION_FAILED:
            throw JSONRPCError(RPC_WALLET_ENCRYPTION_FAILED, error);
        case WalletCreationStatus::SUCCESS:
            break;
        
    }
    UniValue obj(UniValue::VOBJ);
    obj.pushKV("name", wallet->GetName());
    obj.pushKV("warning", Join(warnings, "\n"));
    return obj;
}
static UniValue unloadwallet(const JSONRPCRequest& request)