Remove obsolete po entries - they break translation jobs

The ironic-propose-translation-update job has been failing to update
from transifex because our .po files contain duplicates of obsolete
entries which were causing errors.

Change-Id: I41a056cbe10096c07e7682d8d79ff8f8c58ad3e2
Related-bug: #1298645
Merge "Remove obsolete po entries - they break translation jobs"