Fix Jenkins translation jobs

The jobs keystone-propose-translation-update and
keystone-upstream-translation-update 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.

NOTE: This is NOT a clean backport of the patch from master, but rather
this patch was generated similarly to the patch to master using
https://gist.github.com/dolph/9915293

Closes-Bug: #1299349

Change-Id: Ibbf26bb8158735a5dc57bff7d77a49e00239857c