Remove support for the externalResourcesRequired attribute.

LayoutTests/svg/custom/loadevents-externalresourcesrequired.svg

Index: LayoutTests/svg/custom/loadevents-externalresourcesrequired.svg
diff --git a/LayoutTests/svg/custom/loadevents-externalresourcesrequired.svg b/LayoutTests/svg/custom/loadevents-externalresourcesrequired.svg
deleted file mode 100644
index 40e27bc1a7079d1ff9b9fecfdd030829e74e6014..0000000000000000000000000000000000000000
--- a/LayoutTests/svg/custom/loadevents-externalresourcesrequired.svg
+++ /dev/null
@@ -1,30 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" onload="reportLoadEvent(this);runTest();">
-  <script>
-    <![CDATA[
-      if (window.testRunner)
-        testRunner.dumpAsText();
-
-      var results = new Array();
-
-      function reportLoadEvent(el) {
-		results.push(el.localName);
-      }
-      function runTest()
-      {
-        var test = document.getElementById("console");
-        if ( results.length != 4 || results[0] != "text" ||
-             results[1] != "image" || results[2] != "g" ||
-             results[3] != "svg") {
-          test.appendChild(document.createTextNode("Failed"));
-        } else {
-          test.appendChild(document.createTextNode("Passed"));
-        }
-      }
-    ]]>
-  </script>
-  <g onload="reportLoadEvent(this)">
-    <image externalResourcesRequired="true" id="image" onload="reportLoadEvent(this)" width="100" height="100" xlink:href="resources/green-checker.png" />
-    <text y="130" x="20">This tests load dispatching order with externalResourcesRequired. Bug 16447</text>
-    <text y="150" x="20" id="console" onload="reportLoadEvent(this)"/>
-  </g>
-</svg>