Change license statements (and clean up headers) on some of the files that

Erik or I are primary copyright holders on.

init/halt.c

@@ -4,13 +4,11 @@
  *
  * Copyright 2006 by Rob Landley <rob@landley.net>
  *
- * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
+ * Licensed under GPL version 2, see file LICENSE in this tarball for details.
  */
 
 #include "busybox.h"
-#include <signal.h>
 #include <sys/reboot.h>
-#include <unistd.h>
 
 int halt_main(int argc, char *argv[])
 {