Request transtion when a task is removed

When PIP gets killed via removeRootTasksWithActivityTypes(), no
transition is requested. For non-PIP tasks, processRemoveTask()
is called to remove the task, in which
requestCloseTransitionIfNeeded() is invoked.

But in the case of PIP, removePinnedRootTaskInSurfaceTransaction()
is called but we seem to miss requesting a close transition.

Bug: 275021556
Bug: 273141544
Bug: 272637936
Test: PinnedStackTests
Change-Id: I4c13ecc1b3c1dff15bd0d61aeafeacc1d7705460