Remove more testRunner.display() calls from LayoutTests

LayoutTests/fast/backgrounds/obscured-background-child-style-change-expected.html

 <style>
     .parent {
         position: relative;
         background-color: black;
         width: 100px;
         height: 100px;
     }
     .child {
         position: relative;
         background-color: rgba(0,255,0,0.8);
         width: 100px;
         height: 100px;
     }
     </style>
 <div class=parent>
     <div class=child>
     </div>
 </div>
 <div class=parent>
     <div>
         <div class=child>
         </div>
     </div>
 </div>
 <script>
 document.body.offsetTop;
-if (window.testRunner)
-    testRunner.display();
 var children = document.getElementsByClassName("child");
 children[0].style.backgroundColor = "rgba(0,255,0,0.5)";
 children[1].style.backgroundColor = "rgba(0,255,0,0.5)";
 </script>