[Ongoing Call] Remove the call chip when #onEntryCleanUp is called.

See bug comment #9 for an in-depth explanation.

Test: New unit tests.
Test: I created a test app that sends an ongoing call notification
then removes it 200ms later, and I confirmed that the bug is triggered
without this CL, and is fixed with this CL.
Bug: 199600334

Change-Id: I0f681ccfe55597490bee0d4b190f9fb2c38e28f2