md: remove/add redundancy group only in level change

JIRA: https://issues.redhat.com/browse/RHEL-106845

commit 790abe4
Author: Xiao Ni <xni@redhat.com>
Date:   Wed Jun 11 15:31:08 2025 +0800

    md: remove/add redundancy group only in level change

    del_gendisk is called in synchronous way now. So it doesn't need to handle
    redundancy group in stop path separately.

    Reviewed-by: Yu Kuai <yukuai3@huawei.com>
    Signed-off-by: Xiao Ni <xni@redhat.com>
    Link: https://lore.kernel.org/linux-raid/20250611073108.25463-4-xni@redhat.com
    Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

drivers/md/md.c

@@ -6516,8 +6516,6 @@ static void __md_stop(struct mddev *mddev)
 	if (mddev->private)
 		pers->free(mddev, mddev->private);
 	mddev->private = NULL;
-	if (pers->sync_request && mddev->to_remove == NULL)
-		mddev->to_remove = &md_redundancy_group;
 	put_pers(pers);
 	clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);