Preventing from double remove starting window after Activity destoryed

All client views will be removed after activity destoryed, so and the
starting window. Checking whether the view was detached from window
before remove it from WindowManagerGlobal to prevent the extra remove
calls.

Bug: 286563704
Test: atest StartingSurfaceDrawerTests
Change-Id: Iefd390825fabac2fc1e46b0a9404f9909f159cf9