Don't filter demoted conversation from app subtext

If the notification channel is a demoted converation, we still want to
include it as a notification channel that can bypass DND under the
"apps" preference for DND.

Test: manual, make RunSettingsRoboTests7
Fixes: 152765113
Change-Id: Ief072b19280b0dc6e6c37d2d46d51f045d42bb4e