Bug 1061854 - Dismiss notification swiping up r=mhenretty

With the new ambient indicator, in order to dismiss a notification, a swipe up gesture is needed. All the swipe left code has been removed in this PR.
This only applied to the toaster, and not notifications actually in the utility tray, correct? If so, we should rename the function to indicate that, or if we are removing the function based on my comment below, we should add a comment here saying this is for dismissing the toaster.

Also, maybe I'm reading this wrong, but it looks like if we swipe up on the notification toaster, we will close that notification. Based on https://bugzilla.mozilla.org/show_bug.cgi?id=1061854#c6, I think we want to keep the notification around in both the tray and unread count. Did this change in spec when you were talking to Rob? Or does this code do something entirely different, and I'm just reading it wrong?