Yet another small patch - reorderbuffer.c:1099

Hello

There is weired peace of code in reorderbuffer.c:

```
    /* delete from list of known subxacts */
    if (txn->is_known_as_subxact)
    {
        /* NB: nsubxacts count of parent will be too high now */
        dlist_delete(&txn->node);
    }
    /* delete from LSN ordered list of toplevel TXNs */
    else
    {
        dlist_delete(&txn->node);
    }
```

As you see `if` an `else` branches are exactly the same. I wonder
whether this is a bug or code just requires a bit of cleaning. In the
latter case here is a patch.

According to `git log` both branches were introduced in one commit
b89e1510. I added author and committer of this code to CC since they
have much better understanding of it than I do.

--
Best regards,
Aleksander Alekseev
http://eax.me/