Remove window replacement

It is almost dead code because
- It was added for SurfaceView using a child window.
  But SurfaceView no longer uses a window for years.
- It only executes for 2 conditions:
  - Main window
    - For freeform, there was general change-transition which uses
      a screenshot of window container to animate.
    - For splitscreen, there is TaskOverlay to cover the change.
  - Child window (from ActivityThread r.mPreserveWindow)
    - Server side config change
      Always no-op because config change will clear drawn state
      and then WindowState#hasContentToDisplay return false that
      skips setWillReplaceWindow.
    - Client side calls Activity#recreate.
      But it usually only causes a removal timeout because app
      may not add the child window again.

So no case needs it anymore.

Bug: 163976519
Test: CtsActivityManagerDeviceTestCases

Change-Id: If78155ac453c02cda8bf448bb353061e861747fe