Fix a typo in test_networks.py

Removed redundant 'is'.

TrivialFix

Change-Id: Icb2781a6cc6a59562c808b7f0e1ae1afa19016e4
diff --git a/tempest/api/network/test_networks.py b/tempest/api/network/test_networks.py
index 3825f84..819ef90 100644
--- a/tempest/api/network/test_networks.py
+++ b/tempest/api/network/test_networks.py
@@ -296,7 +296,7 @@
                           subnet_id)
 
         # Since create_subnet adds the subnet to the delete list, and it is
-        # is actually deleted here - this will create and issue, hence remove
+        # actually deleted here - this will create and issue, hence remove
         # it from the list.
         self.subnets.pop()