sched/headers: Remove duplicated includes in kernel/sched/sched.h

Remove duplicated includes of linux/cgroup.h and linux/psi.h. Both of
these includes are included regardless of the config and they are all
protected by ifndef, so no point including them again.

Signed-off-by: GUO Zihua <guozihua@huawei.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230818015633.18370-1-guozihua@huawei.com