Remove English compiled catalogs after compilemessages

./run_tests.sh --compilemessages compiles all languages including
English, but English is the source language and there is no need
to have compiled message catalogs for English.

Also this commit update the description of --makemessages.

Change-Id: I30cf4336cc796e8e3bea71120b6c75ce40aaf888
Closes-Bug: #1261290
Clarify description string for image metric

This metric seems to have an existential crisis.
Change to more succinct "Image existence check"

Change-Id: I953c55214e73bb93c452b25f97960e9637f1008c
Closes-Bug: #1292937
Merge "Clarify description string for image metric"
Merge "Remove English compiled catalogs after compilemessages"