Revert "Navigation ring shortcut.
Fix SystemUI crashing when ther user uninstalls an app previously set as a navigation ring shortcut."

This reverts commit 4108bd3f7d5ec77e45bb86545e924a42c7f0d4d7.
Navring: Fix shortcut for uninstalled app

Fix NPE when the user uninstalls an app that was assigned to a navring
shortcut before.

Change-Id: I3f02fca73cb30e2edbb35d089ad127b35d8233c0