### 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{"loadwallet",
                "\nLoads a wallet from a wallet file or directory."
                "\nNote that all wallet command-line options used when starting bitcoind will be"
                "\napplied to the new wallet (eg -zapwallettxes, upgradewallet, rescan, etc).\n",
                {
                    {"filename", RPCArg::Type::STR, RPCArg::Optional::NO, "The wallet directory or .dat file."},
                },
                RPCResult{