Clear out the taskId when the TaskView is removed

We only have a valid taskId for a bubble if we have a TaskView (hosted
by the expanded view) for it. When a bubble is overflowed, we remove
that task.

These code paths looking for an overflowed bubble with a matching
taskId would never would've been hit in reality since we'd never
have a restart with the same taskId for a bubble in the overflow,
because when a bubble is overflowed, we remove the task.

This CL clears out the taskId when the TaskView is cleaned up and
removes related lookups of overflowed bubbles via taskId.

It might also make sense to do away with mTaskId entirely in a bubble,
but this was added to link tasks to persisted bubbles after a sysui
crash and I'm not entirely certain it's not needed for that still;
tracking investigating that separately in b/415106726.

Flag: EXEMPT bugfix / although most of this is behind com.android.wm.shell.enable_create_any_bubble
Test: atest BubbleTest
Bug: 413473792
Change-Id: I5f188b385824b31db71e68bec417f02d9ae1a153