The overridden url property is no longer necessary.

The issue which the property was circumventing was fixed in django revision https://github.com/django/django/commit/090ff642043a2ca7d69e475f721eab4d68f6572b#django/core/files/storage.py

The overridden property also had the following bug:

If used with storages that return urls that specify the protocol (ex: http://foo.com/bar#comment)
then the protocol separator (:) is also quoted resulting in a broken urls such as: 
http **%3A** //foo.com/bar%23comment