usage.c: remove reference to busybox.h

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

coreutils/install.c

@@ -9,11 +9,12 @@
  *           owner/group, will probably modify bb_make_directory(...)
  */
 
-#include "busybox.h"
-#include "libcoreutils/coreutils.h"
 #include <libgen.h>
 #include <getopt.h> /* struct option */
 
+#include "libbb.h"
+#include "libcoreutils/coreutils.h"
+
 #if ENABLE_FEATURE_INSTALL_LONG_OPTIONS
 static const struct option install_long_options[] = {
 	{ "directory",           0, NULL, 'd' },