sched/headers: Remove <linux/sched.h> from <linux/sched/user.h>

If we add <linux/uidgid.h> then <linux/sched/user.h> becomes a
self-contained header and users of it either don't need <linux/sched.h>
or have already included it.

This reduces the size of the header dependency graph.

Acked-by: Linus Torvalds <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

include/linux/sched/user.h

···
 #ifndef _LINUX_SCHED_USER_H
 #define _LINUX_SCHED_USER_H
 
-#include <linux/sched.h>
+#include <linux/uidgid.h>
+#include <linux/atomic.h>
 
 struct key;