Revert "sched: Fix sched_fork() access an invalid sched_task_group"

hulk inclusion
category: bugfix
bugzilla: 186973, https://gitee.com/openeuler/kernel/issues/I5CA6K


CVE: NA

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This reverts commit 74bd9b82.

Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
Reviewed-by: Chen Hui <judy.chenhui@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>