Remove extraneous const keyword

Originally committed as revision 20263 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/id3v2.h

@@ -58,6 +58,6 @@ extern const AVMetadataConv ff_id3v2_metadata_conv[];
  * A list of ID3v2.4 text information frames.
  * http://www.id3.org/id3v2.4.0-frames
  */
-extern const char const ff_id3v2_tags[][4];
+extern const char ff_id3v2_tags[][4];
 
 #endif /* AVFORMAT_ID3V2_H */