Remove support for the externalResourcesRequired attribute.

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 642961a5807db06828d327863eb3d45df88b96e3..e6ea5f8d9c91a20aa5ccfc7a37cc601a98551179 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -2334,8 +2334,7 @@ void Document::implicitClose()
     // those two functions repeatedly and don't save them on the stack.
 
     // To align the HTML load event and the SVGLoad event for the outermost <svg> element, fire it from
-    // here, instead of doing it from SVGElement::finishedParsingChildren (if externalResourcesRequired="false",
-    // which is the default, for ='true' its fired at a later time, once all external resources finished loading).
+    // here, instead of doing it from SVGElement::finishedParsingChildren.
     if (svgExtensions())
         accessSVGExtensions()->dispatchSVGLoadEventToOutermostSVGElements();