fix webcomponent example issue #7056 (#7057)

* fix webcomponent example issue #7056

* update fix issue #7056, remove unused web component  callbacks

Author: jalexanderfox

examples/webcomponents/index.html

@@ -37,7 +37,7 @@ <h4>Example Details</h4>
 
       // Define WebComponent
       var proto = Object.create(HTMLElement.prototype, {
-        createdCallback: {
+        attachedCallback: {
           value: function() {
             var mountPoint = document.createElement('span');
             this.createShadowRoot().appendChild(mountPoint);