[SB][Screen Chips] Add logs for OngoingCallController.

This adds logs to OngoingCallController (and a bit in
OngoingCallRepository) so that we have the full picture on
call-chip-related events.

This also deletes the UI Events for the call chip, since those aren't
being used.

Bug: 351785188
Bug: 332662551
Flag: com.android.systemui.status_bar_screen_sharing_chips
Test: Start then stop an ongoing call, then dump `OngoingCall` buffer ->
verify logs
Test: atest OngoingCallControllerTest

Change-Id: I5c3e2a518ce1d553487da73ba4aaf0af3bc993ba