Unprefix usage of -webkit-transform in tests

LayoutTests/compositing/geometry/flipped-blocks-inline-mapping.html

 <style>
     .container {
       -webkit-writing-mode: horizontal-bt;
       height: 100px;
       border: 1px solid black;
     }
     div {
       height: 20px;
     }
     .box {
       width: 20px;
       height: 20px;
       background-color: blue;
     }
     
     .transformed {
-      -webkit-transform: translateZ(0);
+      transform: translateZ(0);
     }
     span {
       opacity: 0.8;
     }
     
 </style>
 <div class="container">
     <span>
         <div class="transformed box"></div>
         <div style="display: inline-block">This test should not assert in debug builds</div>
     </span>
 </div>
 <script>
 if (window.testRunner)
   testRunner.dumpAsText();
 </script>