Remove support for the externalResourcesRequired attribute.

LayoutTests/http/tests/svg/load-on-delayed-script.svg

Index: LayoutTests/http/tests/svg/load-on-delayed-script.svg
diff --git a/LayoutTests/http/tests/svg/load-on-delayed-script.svg b/LayoutTests/http/tests/svg/load-on-delayed-script.svg
new file mode 100644
index 0000000000000000000000000000000000000000..1ff4591f7e10abb39df62def8682db8a43f8b408
--- /dev/null
+++ b/LayoutTests/http/tests/svg/load-on-delayed-script.svg
@@ -0,0 +1,24 @@
+<?xml version="1.0" standalone="no"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.0">
+    <!-- script elements should not fire load until fetch is done and script executed -->
+    <text id="console" x="8" y="1.5em">Test didn't run.</text>
+    <script>
+      if (window.testRunner) {
+        testRunner.waitUntilDone();
+        testRunner.dumpAsText();
+      }
+
+      window.onload = function() {
+        if (window.testRunner)
+          testRunner.notifyDone();
+      };
+
+      function runTest() {
+        if (external_script_executed)
+          document.getElementById("console").textContent = "Passed";
+        else
+          document.getElementById("console").textContent = "Failed";
+      }
+    </script>
+    <script xlink:href="resources/delayCachedLoadScript.php" onload="runTest()"/>
+</svg>