Unprefix flexbox tests.

LayoutTests/css3/flexbox/z-index.html

Index: LayoutTests/css3/flexbox/z-index.html
diff --git a/LayoutTests/css3/flexbox/z-index.html b/LayoutTests/css3/flexbox/z-index.html
index 952a413254427ee789a831207233e215ab12d36f..499e686a6ad6b4666930b2811bc6c2994ebbfb99 100644
--- a/LayoutTests/css3/flexbox/z-index.html
+++ b/LayoutTests/css3/flexbox/z-index.html
@@ -13,7 +13,7 @@
 </style>
 <div>This tests that z-index on non-positioned flex-items works. The green boxes should be above the orange boxes, which should be above the purple boxes, which are above the salmon boxes.<div>
 <div style="position:relative">
-    <div style="display:-webkit-flex;">
+    <div style="display:flex;">
         <div class="flex-item" style="z-index: 1; background-color: salmon;"></div>
         <div class="flex-item" style="z-index: 100; background-color: orange;"></div>
     </div>
@@ -21,7 +21,7 @@
     <div class="positioned" style="top: 25px; z-index: 50; background-color: purple"></div>
 </div>
 <div style="position:relative">
-    <div style="display:-webkit-flex;">
+    <div style="display:flex;">
         <img class="flex-item" style="z-index: 1; background-color: salmon;"></img>
         <img class="flex-item" style="z-index: 100; background-color: orange;"></img>
     </div>