Remove the AnnotationUISync service

Its functionality has now been moved into the FrameSync service, except
for the logic that was intended to synchronize the "Show Annotation
Highlights" logic across multiple frames, since this is clearly broken
[1].

The two pieces of functionality related to this we need to support at
the moment are:

 1. The `showHighlights` config option to set whether highlights are
    initially visible.

 2. The highlight toggle button in the sidebar's outer frame

Both of these work without the sidebar app's involvement.

[1] See hypothesis/h#3433 and
    hypothesis/h#3295

h/static/scripts/app.js

@@ -190,7 +190,6 @@ module.exports = angular.module('h', [
 
   .factory('store', require('./store'))
 
-  .value('AnnotationUISync', require('./annotation-ui-sync'))
   .value('Discovery', require('./discovery'))
   .value('ExcerptOverflowMonitor', require('./directive/excerpt-overflow-monitor'))
   .value('VirtualThreadList', require('./virtual-thread-list'))

h/static/scripts/frame-sync.js

@@ -38,8 +38,7 @@ function formatAnnot(ann) {
  * sidebar.
  */
 // @ngInject
-function FrameSync($rootScope, $window, AnnotationUISync, Discovery,
-                   annotationUI, bridge) {
+function FrameSync($rootScope, $window, Discovery, annotationUI, bridge) {
 
   // List of frames currently connected to the sidebar
   var frames = [];
@@ -133,15 +132,6 @@ function FrameSync($rootScope, $window, AnnotationUISync, Discovery,
     bridge.on('sidebarOpened', function () {
       $rootScope.$broadcast('sidebarOpened');
     });
-
-    // Create an instance of the AnnotationUISync class which listens for
-    // selection/focus messages from the frame and propagates them to the rest
-    // of the sidebar app.
-    //
-    // FIXME: The frame message listeners from AnnotationUISync should be
-    // extracted and moved here and then the AnnotationUISync class can be
-    // removed entirely.
-    new AnnotationUISync($rootScope, $window, annotationUI, bridge);
   }
 
   /**