sched: remove redundant on_rq status change

activate_task/deactivate_task will change on_rq status,
no need to do it again.

Signed-off-by: Wang Hui <john.wanghui@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210721091109.1406043-1-john.wanghui@huawei.com