Don't kill PiP with obsolete call to updatePictureInPictureMode

updatePictureInPictureMode() can be called for an activity that's
not on top of the PiP task, and can kill PiP unexpectedly

Bug: 323209868
Test: atest PinnedStackTests#testLaunchTaskByAffinityMatchSingleTask
Change-Id: Iece6ddd7e108986879bd86973f8ec6da82339906