ref: remove cached-property, using django's implementation instead (#16812)

requirements-base.txt

@@ -83,5 +83,4 @@ urllib3==1.24.2
 uwsgi>2.0.0,<2.1.0
 
 # sentry-plugins specific dependencies
-cached-property
 phabricator>=0.6.0,<1.0

src/sentry_plugins/client.py

@@ -6,7 +6,7 @@ import json
 import requests
 
 from bs4 import BeautifulSoup
-from cached_property import cached_property
+from django.utils.functional import cached_property
 from requests.exceptions import ConnectionError, HTTPError
 
 from sentry.http import build_session