Fix unit test for oslo.context 4.1.0

oslo.context 4.1.0 has removed the deprecated field
'tenant' and nova unit test fail as it still expect
the 'tenant' field.

Failure happening in requirements patch while updating the
u-c
- https://review.opendev.org/c/openstack/requirements/+/829599
- http://lists.openstack.org/pipermail/openstack-discuss/2022-February/027455.html

Change-Id: Ia71505026bac121a5dba373c29c29c24f21fcde9

nova/tests/unit/test_context.py

@@ -196,7 +196,6 @@ class ContextTestCase(test.NoDBTestCase):
                            'roles': [],
                            'service_catalog': [],
                            'show_deleted': False,
-                           'tenant': 222,
                            'timestamp': '2015-03-02T22:31:56.641629',
                            'user': 111,
                            'user_domain': None,