Fix duplicated word in lsyscache.c comment - Mailing list pgsql-hackers

While working on a couple of patches that touched lsyscache.c, I noticed a small typo in a comment:

```

 * This is trivially true if they are the same operator. Otherwise,   <==== duplicate “Otherwise"
* Otherwise, we look to see if they both belong to an opfamily that

```

So I’m posting a trivial patch to fix it.

Best regards,