os.h: remove unneeded include

No symbol from platform.h is used in os.h

Change-Id: Ia8f463ab8f9f064fe79f5ee0840b851ae497a080
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.de>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/57936
Original-Reviewed-by:  Felix Singer <felixsinger@posteo.net>
Original-Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72235
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/os.h b/os.h
index ddfa46b..d6fbfe0 100644
--- a/os.h
+++ b/os.h
@@ -17,8 +17,6 @@
  * Header file for OS checking.
  */
 
-#include "platform.h"
-
 // Solaris
 #if defined (__sun) && (defined(__i386) || defined(__amd64))
 #define __FLASHROM_OS__ "SunOS"