Update dreams confirm key flag namespace.

This changelist updates the confirm key handling over dreams flag
namespace to be part of communal, since the dreams namespace is
not ready yet.

Fixes: 326975875
Flag: ACONFIG android.service.dreams.dream_handles_confirm_keys
Test: manual - namespace change
Change-Id: Ia5683422c047896a5e054745c93bbb87f4ab28a4