[Flexiglass] Don't allow NSSL scrolling on the LS

The NSSL was swallowing all touch events in the empty area of the
Placeholder, because it thought that "the scroller wants it". All
scrolling logic should be disabled for the NSSL on the LockScreen.

Bug: 414396116
Test: long tap the empty area in the LS -> wallpaper toast appears
Flag: com.android.systemui.scene_container

Change-Id: Icf81a9b97fde4944c4bd68742e2b095d0a75bffc