Fix snooze not dismissing when it should

Simply check whether the guts is a leavebehind, if it is allow it to
be dismissed.

Test: manual - snooze a notification, touch outside note that it disappears
             - show notification controls on a notification that will
               be removed, note that the controls remain, once 'done' is
               hit the notification is removed
Bug: 63788509
Change-Id: I42c97239f4e3e17f2e69322c94bd8e8f9d7f0737