[flexiglass] Fix multiple smartspace view issue.

There is an issue where, every time we return to the Lockscreen scene,
an additional smartpsace view is added to the smartspace area.

This CL fixes that.

The fix moves the responsibility of removing the views that were added
by KeyguardClockSwitchController into that same class and utilizes a
view tag to identify which children of the smartspace area should be
removed.

Before this, the responsibility for removing the views was in
LockscreenSmartspaceController which was not the same class that was
adding the views (KeyguardClockSwitchController adds the views to the
smartspace area) and has a bug where the smartspace views being tracked
get removed when they're detached, which happens before the old
removeViewsFromParent(...) was invoked.

Bug: 280879610
Test: unit tests pass
Test: manually verified that leaving and returning to the Lockscreen
scene correctly shows only one data-time smartspace view.
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:eedb2b14f54d58fb82f94afa84c5f894e5ea99a6)
Merged-In: I94f16972f3be402cf1a581d6fd2d355bbea5c85e
Change-Id: I94f16972f3be402cf1a581d6fd2d355bbea5c85e