Remove unnecessary assertIn

addCleanup method uses 'id' key for volume type deletion,
so there isn't need to validate that the key exist.

Change-Id: I0741de04dbcc329cf642e58987194c11db9e3a9d
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index 2843222..95ce53a 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -271,10 +271,8 @@
         if backend_name:
             extra_specs = {"volume_backend_name": backend_name}
 
-        body = client.create_volume_type(name=randomized_name,
-                                         extra_specs=extra_specs)
-        volume_type = body['volume_type']
-        self.assertIn('id', volume_type)
+        volume_type = client.create_volume_type(
+            name=randomized_name, extra_specs=extra_specs)['volume_type']
         self.addCleanup(client.delete_volume_type, volume_type['id'])
         return volume_type