Revert "LayoutLib: Fix true transparency in status bar."

This reverts commit 4eb298a9.

Even though this is techinically closer to what the framework does, the
fix is not complete. As a result, it looks worse when using AppCompat
themes. Revert the change for the release.

Change-Id: I67c1002ea17dee7234d78e2d13aab876467bd70f