Replace usages of communal_hub_on_mobile

The isV2FlagEnabled utility method checks both the flag and config
value and is used to gate V2 functionality. The communal_hub_on_mobile
flag is obsolete and we're deprecating it as the naming isn't accurate.

Bug: 380122741
Fixed: 380122741
Test: atest DreamOverlayRegistrantTest DreamOverlayServiceTest GlanceableHubQuickAffordanceConfigTest GlanceableHubContainerControllerTest
Flag: com.android.systemui.glanceable_hub_v2
Change-Id: Ied6e8d0f20ba6b28050eee0464d37c98f414c706