### Body

Currently `start_date` is mandatory parameter.
For DAGs with `schedule=None` we can relax this requirement as no scheduling calculation needed so the `start_date` parameter isn't used.

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
include_dependent_dags=include_subdags,  
            session=session,
            dag_bag=dag_bag,
            exclude_task_ids=exclude_task_ids,
        )
        if dry_run:
            return session.scalars(tis).all()
        tis = session.scalars(tis).all()
        count = len(list(tis))
        do_it = True
        if count == 0:
            return 0
        if confirm_prompt:
            ti_list = "\n".join(str(t) for t in tis)
            question = f"You are about to delete these {count} tasks:\n{ti_list}\n\nAre you sure? [y/n]"
            do_it = utils.helpers.ask_yesno(question)
        if do_it:
            clear_task_instances(
                list(tis),
                session,
                dag=self,
                dag_run_state=dag_run_state,
            )
        else:
            count = 0
            print("Cancelled, nothing was cleared.")
        session.flush()
        return count
    @classmethod
    def clear_dags(