use more boiler plate GPL notices

miscutils/crontab.c

@@ -5,10 +5,9 @@
  * usually setuid root, -c option only works if getuid() == geteuid()
  *
  * Copyright 1994 Matthew Dillon (dillon@apollo.west.oic.com)
- * May be distributed under the GNU General Public License
- *
- * Vladimir Oleynik <dzo@simtreas.ru> (C) 2002 to be used in busybox
+ * Vladimir Oleynik <dzo@simtreas.ru> (C) 2002
  *
+ * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
  */
 
 #include <stdio.h>