remove TextResourceDecoder::detectJapaneseEncoding decl which is never defined

Source/core/html/parser/TextResourceDecoder.h

 /*
     Copyright (C) 1999 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2006 Alexey Proskuryakov (ap@nypop.com)
     Copyright (C) 2006, 2008 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 64 matching lines @@
 private:
     TextResourceDecoder(const String& mimeType, const WTF::TextEncoding& defaultEncoding, bool usesEncodingDetector);
 
     enum ContentType { PlainTextContent, HTMLContent, XMLContent, CSSContent }; // PlainText only checks for BOM.
     static ContentType determineContentType(const String& mimeType);
     static const WTF::TextEncoding& defaultEncoding(ContentType, const WTF::TextEncoding& defaultEncoding);
 
     bool checkForCSSCharset(const char*, size_t, bool& movedDataToBuffer);
     bool checkForXMLCharset(const char*, size_t, bool& movedDataToBuffer);
     void checkForMetaCharset(const char*, size_t);
-    void detectJapaneseEncoding(const char*, size_t);
     bool shouldAutoDetect() const;
 
     ContentType m_contentType;
     WTF::TextEncoding m_encoding;
     OwnPtr<TextCodec> m_codec;
     EncodingSource m_source;
     const char* m_hintEncoding;
     Vector<char> m_buffer;
     bool m_checkedForBOM;
     bool m_checkedForCSSCharset;
     bool m_checkedForXMLCharset;
     bool m_checkedForMetaCharset;
     bool m_useLenientXMLDecoding; // Don't stop on XML decoding errors.
     bool m_sawError;
     bool m_usesEncodingDetector;
 
     OwnPtr<HTMLMetaCharsetParser> m_charsetParser;
 };
 
 }
 
 #endif