Remove the haveItem check for RSS and Atom

The haveItem check for RSS and Atom causes the feeds to act unexpectedly.
For RSS, the checked tags don't necessarily have to be unique.  For atom,
it is allowed to have duplicate items (including duplicated ids) in one feed,
so this shouldn't be stopped either.

If you really want the haveItem functionality, then it should probably parse the feed more completely to remove duplicates.   This would probably mean parsing the date to find which item to actually keep, and for RSS finding a unique key for the item.