### 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
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import collections
import copy
import itertools
import json
import logging
import math
import re
import socket
import sys
import traceback
from collections import defaultdict
from datetime import timedelta
from json import JSONDecodeError
from operator import itemgetter
from typing import Iterable, List, Optional, Tuple
from urllib.parse import parse_qsl, unquote, urlencode, urlparse
import lazy_object_proxy
import markupsafe
import nvd3