examples/cmdline: remove useless headers by the rule IWYU

Signed-off-by: Denis Pronin <dannftk@yandex.ru>

Author: dpronin

examples/cmdline/main.c

@@ -4,10 +4,8 @@
  * All rights reserved.
  */
 
-#include <stdio.h>
-#include <string.h>
 #include <stdint.h>
-#include <errno.h>
+
 #include <sys/queue.h>
 
 #include <cmdline_rdline.h>