Remove duplicated word in av_strlcat() doxy.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@21549 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavutil/avstring.h

@@ -83,7 +83,7 @@ size_t av_strlcat(char *dst, const char *src, size_t size);
 
 /**
  * Append output to a string, according to a format. Never write out of
- * the destination buffer, and and always put a terminating 0 within
+ * the destination buffer, and always put a terminating 0 within
  * the buffer.
  * @param dst destination buffer (string to which the output is
  *  appended)