### 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
"""Customize permission names for FAB's builtin UserDBModelView."""
    _class_permission_name = permissions.RESOURCE_USER
    class_permission_name_mapping = {
        'resetmypassword': permissions.RESOURCE_MY_PASSWORD,
        'resetpasswords': permissions.RESOURCE_PASSWORD,
        'userinfoedit': permissions.RESOURCE_MY_PROFILE,
        'userinfo': permissions.RESOURCE_MY_PROFILE,
    }
    method_permission_name = {
        'add': 'create',
        'download': 'read',
        'show': 'read',
        'list': 'read',
        'edit': 'edit',
        'delete': 'delete',
        'resetmypassword': 'read',
        'resetpasswords': 'read',
        'userinfo': 'read',
        'userinfoedit': 'read',
    }
    base_permissions = [
        permissions.ACTION_CAN_CREATE,
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_EDIT,
        permissions.ACTION_CAN_DELETE,
    ]
    @property
    def class_permission_name(self):