[MTD] Remove unnecessary user space check from mtd.h.

Since the header file include/linux/mtd/mtd.h is not exported to user
space, remove the user space check and error.
Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

include/linux/mtd/mtd.h

@@ -9,10 +9,6 @@
 #ifndef __MTD_MTD_H__
 #define __MTD_MTD_H__
 
-#ifndef __KERNEL__
-#error This is a kernel header. Perhaps include mtd-user.h instead?
-#endif
-
 #include <linux/types.h>
 #include <linux/module.h>
 #include <linux/uio.h>