Prevent onboarding counters from overflow.

We does not unregister the OverviewProxy inside RecentsOnboarding unless user has seen both onboarding tips. If the OverviewProxy does not get unregistered for good, whenever user swipes up from home, we increment the counter that's used to track number of times user has swiped up from home. Though it can be extremely rare, it can overflow.

Change-Id: I43e74b3634eacf3d12c2ce3de23135fdd1d83d24
Fixes: 80202086
Test: N/A