Fix Jenkins translation jobs

The job glance-propose-translation-update
does not update from
transifex since our po files contain duplicate entries where
obsolete entries duplicate normal entries.

Remove all obsolete entries to fix the job.

Add test to pep8 that checks that no new breakages get
introduced.

Change-Id: I1bae1c1bf27bf664b24cf75fc96efb0fcfddc392
Closes-Bug: #1299349
Merge "Fix Jenkins translation jobs"