PSS: Fix MediaProjectionTaskView leaking in KeyguardController

TaskPreviewSizeProvider was registering itself as a configuration
changes listener when created, and never unregistering itself again.
Since a new one is created every time the app chooser is created,
it would create a new leak every time.
The class indirectly references MediaProjectionTaskView, which itself
holds onto large Bitmaps, which can make the leak costly.

Bug: 290754514
Test: Manually - Took heap dump before and after the fix
Test: TaskPreviewSizeProviderTest
Change-Id: Id03d9b3b5a94193f0e5d75a6ff602dd74b45f40c