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.
Thinking about this more, I don't think the `updateNotificationIndicator` function is really working as it is. First of all, the unread boolean we pass in essentially tells the function to do something (ie., if was pass in `false` or undefined, the function will do nothing). So we can remove any calls to this function without the `true` parameter, and the functionality will be unchanged.

But more than this, updating the indicator is inherently tied to `unreadNotifications`. Any time we update the variable, we want to update the indicator. Yes, in `addNotification`, we separate these two without a timeout, but that is really unnecessary. In my mind we are only ever doing two things: 1.) adding one unread notification, 2.) clearing unread notifications. So instead of updating the `unreadNotifications` variable, and then calling either `updateNotificationIndicator` or `hideNotificationIndicator`, let's just have two functions: `addUnreadNotification` and `clearUnreadNotifications`. Inside these functions we can update the `unreadNotifications` count. And we should remove all calls to `updateNotificationIndicator` that didn't pass in `true` for unread.