Remove vanished tasks from repo

When a task vanishes we might mark them as minimized. If that task is
being launched in a different windowing mode, we should remove it from
the repository.

Bug: 369975365
Test: atest DesktopTasksTransitionObserverTest
Flag: com.android.window.flags.enable_desktop_windowing_back_navigation
Change-Id: I252c090e7b690f87223c000840fc41d64f4fb239