Don't use proxy for cors test

Author: niklasvh

tests/cases/images/cross-origin.html

@@ -4,7 +4,7 @@
         <title>External content tests</title>
         <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
         <script>
-            h2cOptions = {useCORS: true};
+            h2cOptions = {useCORS: true, proxy: null};
         </script>
         <script type="text/javascript" src="../../test.js"></script>
     </head>