Remove internalSubset from DocumentType

Source/core/dom/DocumentType.h

Index: Source/core/dom/DocumentType.h
diff --git a/Source/core/dom/DocumentType.h b/Source/core/dom/DocumentType.h
index 50efcec815b4ebd9a7e10d45a5dc24efbd95e8d2..905189545834570fd4428ccddd8c0c85ad923bff 100644
--- a/Source/core/dom/DocumentType.h
+++ b/Source/core/dom/DocumentType.h
@@ -40,7 +40,6 @@ public:
     const String& name() const { return m_name; }
     const String& publicId() const { return m_publicId; }
     const String& systemId() const { return m_systemId; }
-    const String& internalSubset() const { return m_subset; }
 
 private:
     DocumentType(Document*, const String& name, const String& publicId, const String& systemId);
@@ -56,7 +55,6 @@ private:
     String m_name;
     String m_publicId;
     String m_systemId;
-    String m_subset;
 };
 
 DEFINE_NODE_TYPE_CASTS(DocumentType, isDocumentTypeNode());