Disable 'RemoteUserMiddleware' when patching auth

Remove ``'django.contrib.auth.middleware.RemoteUserMiddleware'``, because having it active will automatically log out the webtest user. The reason for this behaviour is that ``WebtestUserBackend`` extends ``RemoteUserBackend``, and the middleware detects it and automatically logs out the user.

See: https://github.com/django/django/blob/master/django/contrib/auth/middleware.py#L125