[SB] Remove status_bar_screen_sharing_chips flag.

This flag was launched in 24Q4, which has been released for a month.

Bug: 332662551
Flag: EXEMPT flag removal
Test: Share screen to app -> verify screen share chip appears with timer
Test: Cast to other device -> verify cast chip appears
Test: Screen record -> verify screenrecord 3-2-1 countdown chip appears
and then timer chip appears
Test: Verify call chip still works
Test: atest OngoingCallControllerTest CollapsedStatusBarFragmentTest

Change-Id: I0c7426924b1c3770efc29a916399780112c78a9c