Neutron: Remove get_namespace from API extensions

Based on the conversation on the ML.

http://lists.openstack.org/pipermail/openstack-dev/2015-June/066219.html

Change-Id: I95a0aba75d10d15a94b0eeaed80a8f7a22b85625
diff --git a/tempest/api/network/test_extensions.py b/tempest/api/network/test_extensions.py
index e9f1bf4..be7174b 100644
--- a/tempest/api/network/test_extensions.py
+++ b/tempest/api/network/test_extensions.py
@@ -57,7 +57,6 @@
             self.assertIn('updated', ext_details.keys())
             self.assertIn('name', ext_details.keys())
             self.assertIn('description', ext_details.keys())
-            self.assertIn('namespace', ext_details.keys())
             self.assertIn('links', ext_details.keys())
             self.assertIn('alias', ext_details.keys())
             self.assertEqual(ext_details['name'], ext_name)