fix: 404 error related to removed dependency

Remove the broken reference to "elements-demo-resources/ga.js" which is not used anymore.

index.html

@@ -6,7 +6,6 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>vaadin-icons</title>
 
-  <script src="../elements-demo-resources/ga.js"></script>
   <script src="../webcomponentsjs/webcomponents-lite.js"></script>
   <link rel="import" href="../polymer/polymer.html">
   <link rel="import" href="../iron-component-page/iron-component-page.html">