Remove '\p', '\c' and '\e' doxygen markup from doxy, as it should

improve plain text doxy readability.

See the thread: "[RFC] Should we use doxygen markup?".

Originally committed as revision 19122 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/log.h

@@ -39,7 +39,7 @@ struct AVCLASS {
 
     /**
      * A pointer to a function which returns the name of a context
-     * instance \p ctx associated with the class.
+     * instance ctx associated with the class.
      */
     const char* (*item_name)(void* ctx);