Remove empty default for tile list

This was causing a frame of empty list of tiles when expanding to QS,
which translated to big recomposition on the second frame.

Test: manual, perfetto
Flag: com.android.systemui.qs_ui_refactor_compose_fragment
Bug: 389985793
Change-Id: I2838341c3ff4f8f49fbff2f3ef7d21fba4736fb9