Remove minimized tasks when there are only minimized Tasks left.

Remove leftover minimized tasks when the last visible desktop task is
removed to avoid keeping minimized tasks around for the next desktop
session.

Flag: com.android.window.flags.enable_desktop_windowing_task_limit
Bug: 349542123
Test: add 5 tasks, remove all visible ones -> minimized task removed
Test: DesktopTasksLimiterTest
Change-Id: If8a3759370e881b36c2d7e17206c73c8de4e62b8