Unprefix usage of -webkit-transform in tests

LayoutTests/animations/resources/dynamic-stylesheet-insertion-main.css

 body {
   width: 320px;
   height: 480px;
 }
 
 #splash {
   position: absolute;
   left: 20px;
   left: 60px;
   width: 100px;
   height: 100px;
   background-color: blue;
-  -webkit-transform: translate3d(0,80px,0);
+  transform: translate3d(0,80px,0);
   -webkit-animation-name: splashdown;
   -webkit-animation-duration: 0.6s;
   -webkit-animation-delay: 0.1s;
 }
 
 @-webkit-keyframes splashdown {
   0% {
-    -webkit-transform: translate3d(0, -300px, 0);
+    transform: translate3d(0, -300px, 0);
   }
   30% {
     -webkit-animation-timing-function: ease-in;
-    -webkit-transform: translate3d(0, 20px, 0);
+    transform: translate3d(0, 20px, 0);
   }
   40% {
     -webkit-animation-timing-function: ease-in-out;
-    -webkit-transform: translate3d(0, 100px, 0);
+    transform: translate3d(0, 100px, 0);
   }
   90% {
-    -webkit-transform: translate3d(0, 100px, 0);
+    transform: translate3d(0, 100px, 0);
   }
   100% {
-    -webkit-transform: translate3d(0, 100px, 0);
+    transform: translate3d(0, 100px, 0);
   }
 }