Remove support for the externalResourcesRequired attribute.

Source/core/svg/SVGSVGElement.idl

 /*
  * Copyright (C) 2004, 2005 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2010 Rob Buis <buis@kde.org>
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  * Copyright (C) 2006 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 51 matching lines @@
     SVGLength createSVGLength();
     SVGAngle createSVGAngle();
     SVGPoint createSVGPoint();
     SVGMatrix createSVGMatrix();
     SVGRect createSVGRect();
     SVGTransform createSVGTransform();
     SVGTransform createSVGTransformFromMatrix([Default=Undefined] optional SVGMatrix matrix);
     Element getElementById([Default=Undefined] optional DOMString elementId);
 };
 
-SVGSVGElement implements SVGExternalResourcesRequired;
 SVGSVGElement implements SVGFitToViewBox;
 SVGSVGElement implements SVGZoomAndPan;