Fix unable to toggle off Pause app activity

The "Pause app activity if unused" SwitchPreference under App info page.

Currently, the preference controller updates the UI state in the
onOpChanged(), which is unnecessary and is called in another non-UI
thread.

Not updating state in onOpChanged() to fix.

Note: This controller implements the LifecycleObserver to handle
lifecycle related logic, but it's actually a no-op before change
If9e48e44267de8e89a5e8f45d256719130936320. So it used to work fine
without the OnOpChangedListener, we can remove it now.

Fix: 227762370
Test: manual
Change-Id: I33f1f55a706407d7b409c3544f9889c45855b34d