Remove visible notif + summary before NMS.onClick

The onDismiss callback was being called after NMS had handled the
onClick and cancelled the notification already. This would result in the
parent (group summary) not being removed from the UI.

Test: atest SystemUITests
Test: manual
  1. Install go/notify-apk
  2. Post auto-cancellable notification group with two children
  3. Click on notification from the posted group
  Observe: notification is removed; there is still one notification left
  in the group
  4. Click on the last notification
  Observe: group is gone
Fixes: 171467963
Change-Id: Ia0dbc6f12b99c9193cc9355d2fa2b60eb460e0bf