Remove some dead code from html/

Source/core/html/PluginDocument.h

 /*
  * Copyright (C) 2006, 2008, 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 28 matching lines @@
         return adoptRef(new PluginDocument(initializer));
     }
 
     void setPluginNode(Node* pluginNode) { m_pluginNode = pluginNode; }
 
     Widget* pluginWidget();
     Node* pluginNode();
 
     virtual void detach(const AttachContext& = AttachContext()) OVERRIDE;
 
-    void cancelManualPluginLoad();
-
     bool shouldLoadPluginManually() { return m_shouldLoadPluginManually; }
 
 private:
     PluginDocument(const DocumentInit&);
 
     virtual PassRefPtr<DocumentParser> createParser() OVERRIDE;
 
     void setShouldLoadPluginManually(bool loadManually) { m_shouldLoadPluginManually = loadManually; }
 
     bool m_shouldLoadPluginManually;
     RefPtr<Node> m_pluginNode;
 };
 
 DEFINE_DOCUMENT_TYPE_CASTS(PluginDocument);
 
 }
 
 #endif // PluginDocument_h