Remove extern int hz; use proper include file instead.

sys/compat/linux/linux_emul.c

@@ -34,6 +34,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/imgact.h>
+#include <sys/kernel.h>
 #include <sys/lock.h>
 #include <sys/malloc.h>
 #include <sys/mutex.h>
@@ -279,8 +280,6 @@ linux_proc_exec(void *arg __unused, struct proc *p, struct image_params *imgp)
 	}
 }
 
-extern int hz;				/* in subr_param.c */
-
 void
 linux_schedtail(void *arg __unused, struct proc *p)
 {