Explicitly remove the task when a bubble is dismissed

This prevents bubble-hosted tasks from appearing within recents.

RecentTasks filters bubble-hosted tasks while active by checking
the associated display in isUserVisibleRecent. After destroying,
the display (virtual display) is removed so the check no longer
works. Removing the task explicitly when dismissing solves this.

Test: manually, dismiss bubble, check recents
Bug: 131692350
Change-Id: Ia46e70ebba7095571457e1e4c8b2959263fc6828