Remove obsolete Aconfig flag com.android.systemui.status_bar_connected_displays

The flag usage was removed in ag/31235793.

Change-Id: Ib7732e5f6372f7753b640993c2d0d12d56fa9e2b
Test: current tests pass
Flag: com.android.systemui.shared.status_bar_connected_displays
Bug: 382031216