**Apache Airflow version**: 2.1.0

**What happened**:

We use a python script that reads JSON configs from db to dynamically generate DAGs. Sometimes, when JSON Configs is updated, we expect DAGs to be removed in Airflow.  This doesn't always happen. From my observation, one of the following happens:
1) DAG is removed because the python script no longer generates it.
2) DAG still exists but run history is empty. When trigger the DAG, first task is stuck in `queued` status indefinitely.

**What you expected to happen**:
I expect the right behavior should be 
>1) DAG is removed because the python script no longer generates it.

**How to reproduce it**:
* Create a python script in DAG folder that dynamically generates multiple DAGs
* Execute these dynamically generated DAGs a few times
* Use Airflow Variable to toggle (reduce) the # of DAGs generated
* Examine if number of dynamically generated DAGs in the web UI


airflow/models/dag.py
self,
        last_automated_dagrun: Union[None, datetime, DataInterval],
        *,
        restricted: bool = True,
    ) -> Optional[DagRunInfo]:
        """Get information about the next DagRun of this dag after ``date_last_automated_dagrun``.
        This calculates what time interval the next DagRun should operate on
        (its execution date), and when it can be scheduled, , according to the
        dag's timetable, start_date, end_date, etc. This doesn't check max
        active run or any other "max_active_tasks" type limits, but only
        performs calculations based on the various date and interval fields of
        this dag and its tasks.
        :param date_last_automated_dagrun: The ``max(execution_date)`` of
            existing "automated" DagRuns for this dag (scheduled or backfill,
            but not manual).
        :param restricted: If set to *False* (default is *True*), ignore
            ``start_date``, ``end_date``, and ``catchup`` specified on the DAG
            or tasks.
        :return: DagRunInfo of the next dagrun, or None if a dagrun is not
            going to be scheduled.
        """
        
        if self.is_subdag:
            return None
        if isinstance(last_automated_dagrun, datetime):
            warnings.warn(
                "Passing a datetime to DAG.next_dagrun_info is deprecated. Use a DataInterval instead.",
                DeprecationWarning,
                stacklevel=2,