Internal cleanup of window manager

- Remove unnecessary wrapper methods which were used
  for cross package access.
- WindowContainer is associated with display, it doesn't
  need to lookup again by WindowAnimator to update
  pendingLayoutChanges of DisplayContent.
- Remove unused methods and fields.
- Correct some locks in ActivityTaskManagerService.

Fix: 141248611
Test: go/wm-smoke

Change-Id: I5d5dbc9036f6edbfdf87fe5fb7883793def8836e