selftests/sched_ext: Remove duplicate sched.h header

JIRA: https://issues.redhat.com/browse/RHEL-111810

commit e69980b
Author: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Date:   Fri Jul 25 17:04:12 2025 +0800

    selftests/sched_ext: Remove duplicate sched.h header

    ./tools/testing/selftests/sched_ext/hotplug.c: sched.h is included more than once.

    Reported-by: Abaci Robot <abaci@linux.alibaba.com>
    Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=22941
    Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
    Acked-by: Andrea Righi <arighi@nvidia.com>
    Signed-off-by: Tejun Heo <tj@kernel.org>

Signed-off-by: Phil Auld <pauld@redhat.com>

Author: auldp

tools/testing/selftests/sched_ext/hotplug.c

@@ -6,7 +6,6 @@
 #include <bpf/bpf.h>
 #include <sched.h>
 #include <scx/common.h>
-#include <sched.h>
 #include <sys/wait.h>
 #include <unistd.h>