Do not count suppressed group summaries when checking for notifications.

This fixes a bug where a group summary of a bubble (which may not itself be a bubble) is counted as a notification for the purposes of determining if the "Clear All" button (or footer generally) should be shown, even though that notification is not shown or counted when determining if the empty shade view should be displayed.

Fixes: 195822405
Test: NotificationStackScrollerControllerTest
Test: Clear all notifications, go/use-bubbles, post 4 bubbles, read all 4 bubbles, expand shade
Change-Id: I080d5c5ab6f6f48d9dd0f3e46ba48da4ca1e6e60