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

diff --git a/procps/free.c b/procps/free.c
index 2b205d0..42193fd 100644
--- a/procps/free.c
+++ b/procps/free.c
@@ -9,7 +9,7 @@
 
 /* getopt not needed */
 
-#include "busybox.h"
+#include "libbb.h"
 
 int free_main(int argc, char **argv);
 int free_main(int argc, char **argv)