[core] RAY_task_retry_delay_ms has already been publicly documented

[kevin85421]

Why are these changes needed?

https://docs.ray.io/en/latest/ray-core/fault_tolerance/actors.html#unavailable-actors

If a task has max_task_retries > 0 and it received ActorUnavailableError, Ray will retry the task up to max_task_retries times. If the actor is restarting in its constructor, the task retry will fail, consuming one retry count. If there are still retries remaining, Ray will retry again after RAY_task_retry_delay_ms, until all retries are consumed or the actor is ready to accept tasks. If the constructor takes a long time to run, consider increasing max_task_retries or increase RAY_task_retry_delay_ms.

RAY_task_retry_delay_ms has already been publicly documented for years. Therefore, it should not be removed.

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