Remove all mostly untranslated PO files

We now only import PO files that are at least 75 % translated,
so we can delete now all other PO files. The patch only
removes the mostly untranslated files. Once a file becomes mostly
translated, the bot will import it again.

This patch leaves the mostly translated languages Chinese (China),
German, French, Spanish, Australian English as well as US English in.

Change-Id: Ie5d8071817543f064873532ae2d0f7a395d4e316
Closes-Bug: #1317794