Fix Jenkins translation jobs

The -propose-translation-update and -upstream-translation-update
jobs do not update from transifex since our po files contain
duplicate entries where obsolete entries duplicate normal entries.

Remove all obsolete entries to fix the jobs.

Change-Id: I6557c0b0c5ed73a0f87107214f5375ef1d0f8675
Closes-Bug: #1299349
Merge "Fix Jenkins translation jobs" into milestone-proposed