Remove some dead code

- Shell transition no longer adds records into mClosingApps
  and mOpeningApps. But ActivityRecord#getOrientation still works
  so far. So legacy transition also doesn't need the condition.
  Ideally isVisibleRequested() should has the same meaning to
  identify "closing".
- labelRes/icon are used for legacy starting window in core.
  Now the fields are no longer read.
- Remove duplicated code in WindowState#prepareSync which is
  caused by merge error from downstream.
- info and info.applicationInfo are non-null. Other places always
  access them directly.

Bug: 163976519
Test: CtsWindowManagerDeviceActivity
Change-Id: I8c6a2709bfc6f300b94c149ba3577978c81719a5