Remove name checking for api version 1

Since cinder api version 1 is deprecated, it's redundant
to check 'display_name' field.

Change-Id: I17f610994f496da246dae0c5b77c20ab32f19218
diff --git a/tempest/scenario/test_stamp_pattern.py b/tempest/scenario/test_stamp_pattern.py
index 96b423d..5f5d701 100644
--- a/tempest/scenario/test_stamp_pattern.py
+++ b/tempest/scenario/test_stamp_pattern.py
@@ -68,10 +68,7 @@
                                                 volume['id'], 'available')
         waiters.wait_for_volume_resource_status(self.snapshots_client,
                                                 snapshot['id'], 'available')
-        if 'display_name' in snapshot:
-            self.assertEqual(snapshot_name, snapshot['display_name'])
-        else:
-            self.assertEqual(snapshot_name, snapshot['name'])
+        self.assertEqual(snapshot_name, snapshot['name'])
         return snapshot
 
     def _wait_for_volume_available_on_the_system(self, ip_address,