Simplify annotation card focusing logic

Don't bother looking up the annotations (for the tags),
since we only need the list of tags anyway.

(It was different when we worked with the IDs, but we
moved to use tags instead, so the actual annotations
are no longer needed.)

h/static/scripts/services.coffee

@@ -166,8 +166,7 @@ class Hypothesis extends Annotator
 
     .bind('setFocusState', (ctx, data) =>
       @element.scope().$apply =>
-        annotations = this._getLocalAnnotations data.tags
-        this.setViewerFocusState annotations, data.state
+        this.setViewerFocusState data.tags, data.state
     )
 
     .bind('toggleViewerSelection', (ctx, tags=[]) =>
@@ -237,14 +236,14 @@ class Hypothesis extends Annotator
     @_setSelectedAnnotations selected
     this
 
-  setViewerFocusState: (annotations, state) ->
+  setViewerFocusState: (tags, state) ->
     scope = @element.scope()
     focused = scope.focusedAnnotations ?= {}
-    for a in annotations
+    for tag in tags
       if state
-        focused[a.$$tag] = true
+        focused[tag] = true
       else
-        delete focused[a.$$tag]
+        delete focused[tag]
     this
 
   updateViewer: (annotations=[]) ->