Reset "show system apps" state upon leaving screen

Ensure that if the user navigates away from the Permission Apps screen,
that system apps will be hidden upon returning to the screen.

Test: Naviage to a Permission apps screen, select "show system apps",
navigate away, then navigate back. System apps should be hidden.

Change-Id: Ib953719b58b37dc2741f7e97a04674e2d8f5b7eb