[flexiglass] Removes redundant notifications property

The QS scene is injected with the NotificationsPlaceholderViewModel so
it doesn't need to get it from the view-model.

Bug: 354270224
Test: NONE this is but a simple change, the next CL tests things really
Flag: com.android.systemui.scene_container
Change-Id: I99380a78ae9e53b80327dbc0ec662d5916c895eb