CSS manual tests: reduce usage of webkit prefix

third_party/WebKit/ManualTests/transitions.html

 <style>
     div {
         width: 50px;
         height: 50px;
         background-color: yellow;
     }
 
     div.green {
         width: 100px;
         background-color: green;
-        -webkit-transition-property: background-color;
-        -webkit-transition-duration: 5s;
+        transition-property: background-color;
+        transition-duration: 5s;
     }
 
     div.square {
         width: 100px;
         height: 100px;
-        -webkit-transition-property: height;
-        -webkit-transition-duration: 2s;
+        transition-property: height;
+        transition-duration: 2s;
     }
 </style>
 <p id="instructions">
     When you click the Change button, the shape will
     <span id="description"></span>.
     <button style="display: block;" onclick="transition()">Change</button>
 </p>
 <div id="target"></div>
 <script>
     var state = 0;
@@ skipping 15 matching lines @@
         var target = document.getElementById("target");
         target.className = transitions[state].className;
         state++;
         if (state < transitions.length)
             document.getElementById("description").innerText = transitions[state].description;
         else {
             document.getElementById("instructions").innerText = "Done.";
         }
     }
 </script>