remove TextResourceDecoder::detectJapaneseEncoding decl which is never defined

Source/core/html/parser/TextResourceDecoder.h

Index: Source/core/html/parser/TextResourceDecoder.h
diff --git a/Source/core/html/parser/TextResourceDecoder.h b/Source/core/html/parser/TextResourceDecoder.h
index ee76a4ee581df04f2a049634632f5c3d1a2770f0..c8a55813fe551c87ad38d56deaf87df9a17ba0a0 100644
--- a/Source/core/html/parser/TextResourceDecoder.h
+++ b/Source/core/html/parser/TextResourceDecoder.h
@@ -82,7 +82,6 @@ private:
     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;