Fix issue #6717667: expanded notification actions don't work on the lock screen

FLAG_ACTIVITY_CLOSE_SYSTEM_DIALOGS was a mistake.

Instead, and the infrastructure for the status bar to take care
of closing and hiding things itself when you press these buttons,
just like it does for the main Intent of the notification.

Bug: 6717667
Change-Id: I1b22186e0cedc05f46a1a3ec78053a72afaf61b1