Remove redundant file descriptions from copyright headers.

File description is only kept in the @file doxy.

Originally committed as revision 22840 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/eval.c

 /*
- * simple arithmetic expression evaluator
- *
  * Copyright (c) 2002-2006 Michael Niedermayer <michaelni@gmx.at>
  * Copyright (c) 2006 Oded Shimon <ods15@ods15.dyndns.org>
  *

libavcodec/eval.h

 /*
- * simple arithmetic expression evaluator
- *
  * Copyright (c) 2002 Michael Niedermayer <michaelni@gmx.at>
  *
  * This file is part of FFmpeg.
@@ -22,7 +20,7 @@
 
 /**
  * @file libavcodec/eval.h
- * eval header.
+ * simple arithmetic expression evaluator
  */
 
 #ifndef AVCODEC_EVAL_H