Fixed pinned stack lockscreen interaction

- Use focused stack to determine of an activity can occlude the
lockscreen instead of the topmost stack. The topmost stack should be the
pinned stack which we don't want to decide if the lockscreen should be
occluded. Should be based on the stack that can contain a resume
activity.
- Make sure the remove AppWindowToken from the display if some one ever
calls removeImmediately() directly on it. This makes sure internal
states are clean-up correctly if the removal wasn't triggered from the
AM side.
- Remove some logs that end up causing confusion for testers thinking
something is broken.

Change-Id: I635f6c9a372882ff33d2e9780a1407f78cddf457
Fixes: 37208509
Test: android.server.cts.KeyguardLockedTests#testShowWhenLockedActivityAndPipActivity
Test: android.server.cts.KeyguardLockedTests#testShowWhenLockedPipActivity