**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
"""
        Given a list of dag_ids, get a set of Paused Dag Ids
        :param dag_ids: List of Dag ids
        :param session: ORM Session
        :return: Paused Dag_ids
        """
        paused_dag_ids = (
            session.query(DagModel.dag_id)
            .filter(DagModel.is_paused == expression.true())
            .filter(DagModel.dag_id.in_(dag_ids))
            .all()
        )
        paused_dag_ids = {paused_dag_id for paused_dag_id, in paused_dag_ids}
        return paused_dag_ids
    def get_default_view(self) -> str:
        """
        Get the Default DAG View, returns the default config value if DagModel does not
        have a value
        """
        
        return self.default_view or conf.get('webserver', 'dag_default_view').lower()
    @property
    def safe_dag_id(self):
        return self.dag_id.replace('.', '__dot__')
    @property
    def relative_fileloc(self) -> Optional[pathlib.Path]: