usage.c: remove reference to busybox.h

*: s/include "busybox.h"/include "libbb.h"

debianutils/run_parts.c

@@ -30,10 +30,10 @@
  * -u MASK		umask. Set the umask of the program executed to MASK.
  */
 
-
-#include "busybox.h"
 #include <getopt.h>
 
+#include "libbb.h"
+
 #if ENABLE_FEATURE_RUN_PARTS_LONG_OPTIONS
 static const struct option runparts_long_options[] = {
 	{ "arg",        1,      NULL,   'a' },