Fix CTS test case failure

android.accessibilityservice.cts.AccessibilityEmbeddedDisplayTest#
testA11yWindowNotifyWhenResizeWindowInActivityViewAfterServiceOffAndOn

Removing the windowsForA11yObserver of embedded displays when
removing the windowsForA11yObserver of its parent display because the
windowsForA11yObserver is the same of them.

Bug: 153342178
Test: a11y CTS & unit tests
Test: atest --iterations 20 AccessibilityEmbeddedDisplayTest

Change-Id: Idd21692cc599b565219e1cd3960d0cee3298e66b