Ensure that transitions are unregistered when the launchable is detached.

Ephemeral return animations are registered as remote transitions, and
unregistered after they run once. But if they're never run they risk
leaking, so we unregister them once the view they use is detached or the
composable is not being composed anymore.

This will help with usages of the library outside of Launcher (and maybe
Launcher itself in the future).

Bug: 339194555
Flag: com.android.systemui.shared.return_animation_framework_library
Test: manual
Change-Id: I28011978589e2dd840326539d79dfd0e09246e13