Cleanup video provider binder code.

1. Ensure we always unlink for death from the VideoCallImpl.
2. Ensure we compare the binders in the Call instance properly so that
we are not always replacing the VideoCallImpl used.
3. Ensure we cleanup the VideoCallImpl when its being removed.

Test: Manual testing of video calls for regressions.
Bug: 121156974
Change-Id: I440e8fb4ab9a5051ee02358933c495de736e2bd0