Themes: Remove an app's icons from cache when installing

If an app is being updated then its icons will exist in cache. Go ahead
and delete them so that they can be recreated.

Change-Id: If0ee4388efd4aa146ebcdc46b1b0742f0852bad3
(cherry picked from commit 91cabc9b9006e8c2f06aa6cbbc237c4ca585e49d)