Don't abbreviate duplicate merge failed messages

We are now only sending duplicate change emails once a day, so
repeating ourselves that often isn't too noisy. Also, isAlreadySent
and isDuplicate were repeating the relatively expensive operation of
listing all messages for a change, and there's no need to do that work
twice.

Change-Id: Ib92e584d9290df43632374f34327a153192ad14a
1 file changed