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

diff --git a/procps/pidof.c b/procps/pidof.c
index ea2520a..3541aee 100644
--- a/procps/pidof.c
+++ b/procps/pidof.c
@@ -7,7 +7,7 @@
  * Licensed under the GPL version 2, see the file LICENSE in this tarball.
  */
 
-#include "busybox.h"
+#include "libbb.h"
 
 enum {
 	USE_FEATURE_PIDOF_SINGLE(OPTBIT_SINGLE,)