Remove unnecessary tuple return type

The tuple return type of addCommonscat() has been unnecessary since 2010.
https://www.mediawiki.org/wiki/Special:Code/pywikipedia/8548
Returned (status, always) were unused variables.

Change-Id: I767c00ea8b500dc955c1f80b626a076c1c330510
Merge "Remove unnecessary tuple return type"