Don't show update in the DOM on AJAX error.

cms/static/js/views/course_info_edit.js

@@ -101,9 +101,13 @@ CMS.Views.ClassInfoUpdateView = Backbone.View.extend({
             title: gettext('Saving') + '…'
         });
         saving.show();
+        var ele = this.modelDom(event);
         targetModel.save({}, {
             success: function() {
                 saving.hide();
+            },
+            error: function() {
+                ele.remove();
             }
         });
         this.closeEditor(this);