Cleanup the content overlay

Cleanup the content overlay forcefully in case it's littering due to
unhandled shell transition. This serves as a last resort to make sure no
visual impact to the user, i.e. not a root fix.

Before: http://recall/-/aaaaaabFQoRHlzixHdtY/bU2hzKgIriCrKrkLdGRO2P
After: http://recall/-/aaaaaabFQoRHlzixHdtY/cN5M30IaQzbuxajy7PBqIH
Bug: 330488822
Test: manully, follow the reproduce path. see also videos
Change-Id: I60c4482fc8783e70f38fe2a7f693d7a14f937541