Remove use_mox usage

As of horizon 14.0.0.0b2 or later the use_mox directive is unecessary
because use_mox defaults to False, so we can remove it.

Change-Id: If7109c998b791bca0c3a19e0ff7a65a086d510f4

lower-constraints.txt

@@ -46,7 +46,6 @@ MarkupSafe==1.0
 mccabe==0.2.1
 mock==2.0.0
 monotonic==0.6
-mox3==0.20.0
 msgpack-python==0.4.0
 munch==2.1.0
 netaddr==0.7.18

neutron_vpnaas_dashboard/dashboards/project/vpn/tests.py

@@ -26,8 +26,6 @@ from neutron_vpnaas_dashboard.test import helpers as test
 
 class VPNTests(test.TestCase):
 
-    use_mox = False
-
     class AttributeDict(dict):
         def __getattr__(self, attr):
             return self[attr]

neutron_vpnaas_dashboard/test/api_tests/test_vpnaas.py

@@ -23,8 +23,6 @@ neutronclient = client.Client
 
 class VPNaasApiTests(test.APITestCase):
 
-    use_mox = False
-
     @helpers.create_mocks({neutronclient: ('create_vpnservice',)})
     def test_vpnservice_create(self):
         vpnservice1 = self.api_vpnservices.first()