Unprefix usage of -webkit-transform in tests

LayoutTests/css3/filters/filter-with-transform.html

 <style>
 div {
     width: 200px;
     height: 200px;
     background-color: red;
     margin-left:40px;
     margin-top:40px;
-    -webkit-transform: rotate(-30deg);
+    transform: rotate(-30deg);
     -webkit-filter: hue-rotate(100deg);
 }
 </style>
 <div>
   <!-- This paragraph will have a filter applied. -->
 </div>
 <script>
 if (window.testRunner)
     window.testRunner.dumpAsTextWithPixelResults();
 </script>