usage.c: remove reference to busybox.h
*: s/include "busybox.h"/include "libbb.h"

diff --git a/debianutils/which.c b/debianutils/which.c
index 02992d0..2c71ed3 100644
--- a/debianutils/which.c
+++ b/debianutils/which.c
@@ -10,7 +10,7 @@
  * Based on which from debianutils
  */
 
-#include "busybox.h"
+#include "libbb.h"
 
 int which_main(int argc, char **argv);
 int which_main(int argc, char **argv)