### Description

The stable REST API seems to be missing the functionality to delete a DAG. 
This would mirror clicking the "Trash Can" on the UI (and could maybe eventually power it)

![image](https://user-images.githubusercontent.com/80706212/131702280-2a8d0d74-6388-4b84-84c1-efabdf640cde.png)


### Use case/motivation

_No response_

### Related issues

_No response_

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

airflow/www/views.py
"""Default filters for model"""
        return (
            super()
            .get_query()
            .filter(or_(models.DagModel.is_active, models.DagModel.is_paused))
            .filter(~models.DagModel.is_subdag)
        )
    def get_count_query(self):
        """Default filters for model"""
        return super().get_count_query().filter(models.DagModel.is_active).filter(~models.DagModel.is_subdag)
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
        ]
    )
    @provide_session
    @expose('/autocomplete')
    def autocomplete(self, session=None):