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/opt.h

@@ -23,7 +23,7 @@
 #define AVCODEC_OPT_H
 
 /**
- * @file libavcodec/opt.h
+ * @file
  * AVOptions
  */