### 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

if (pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Cannot set a HD seed to a wallet with private keys disabled");
    }
    auto locked_chain = pwallet->chain().lock();
    LOCK(pwallet->cs_wallet);
    
    if (!pwallet->CanSupportFeature(FEATURE_HD)) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Cannot set a HD seed on a non-HD wallet. Start with -upgradewallet in order to upgrade a non-HD wallet to HD");
    }
    EnsureWalletIsUnlocked(pwallet);
    bool flush_key_pool = true;
    if (!request.params[0].isNull()) {
        flush_key_pool = request.params[0].get_bool();
    }
    CPubKey master_pub_key;
    if (request.params[1].isNull()) {
        master_pub_key = pwallet->GenerateNewSeed();
    } else {
        CKey key = DecodeSecret(request.params[1].get_str());
        if (!key.IsValid()) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid private key");
        }
        if (HaveKey(*pwallet, key)) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Already have this key (either as an HD seed or as a loose private key)");
        }
        master_pub_key = pwallet->DeriveNewSeed(key);
    }
    pwallet->SetHDSeed(master_pub_key);
    if (flush_key_pool) pwallet->NewKeyPool();
    return NullUniValue;