Reduce unnecessary invocation of updateKeepClearAreas

The one in performSurfacePlacementNoTrace should be enough.

- The calculation relies on bounds and window frames. The changes of
  focus, insets control won't affect the result.
- If display size changes, performSurfacePlacement is guaranteed to
  be called (remove the invocation in onDisplayChanged).
- Add missing Region.recycle.

Bug: 159103089
Test: atest KeepClearRectsTests
Change-Id: I45571944cc0dc8e425daa506bd0752081df571e8