Remove duplicated includes in stdlib.h and termios.h

OK guenther@

src/include/stdlib.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: stdlib.h,v 1.66 2016/09/09 18:12:37 millert Exp $	*/
+/*	$OpenBSD: stdlib.h,v 1.67 2016/09/20 21:10:22 fcambus Exp $	*/
 /*	$NetBSD: stdlib.h,v 1.25 1995/12/27 21:19:08 jtc Exp $	*/
 
 /*-
@@ -85,8 +85,6 @@ typedef struct {
 extern size_t	__mb_cur_max;
 #define	MB_CUR_MAX	__mb_cur_max
 
-#include <sys/cdefs.h>
-
 /*
  * Some header files may define an abs macro.
  * If defined, undef it to prevent a syntax error and issue a warning.