Remove explicit filename from Doxygen @file commands.

Passing an explicit filename to this command is only necessary if the
documentation in the @file block refers to a file different from the
one the block resides in.

Originally committed as revision 22921 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/vorbis_dec.c

@@ -1,5 +1,5 @@
 /**
- * @file libavcodec/vorbis_dec.c
+ * @file
  * Vorbis I decoder
  * @author Denes Balatoni  ( dbalatoni programozo hu )
  *