Revert "Use theme change categories and clear widget preview cache"

This reverts commit b52694e4fdd3c8ee524b5f6f870697e40061b2a6.

Change-Id: I69bff363280ea69ee83dea3a8f2ef2d0d95a7be0
Revert "Handle theme changes"

This reverts commit 64718d775ce8322915d143adb9a0f1ea3160e9e3.

Change-Id: Ibf92232dfa8ee96aafecc4b4e49fc55cfb21c229