CORD-879 eliminate unnecessary import of Subscriber model

Change-Id: I0496bdefe20fb97d52400dc4cd8d51730baf0947
diff --git a/xos/models.py b/xos/models.py
index b5e9303..abec34a 100644
--- a/xos/models.py
+++ b/xos/models.py
@@ -1,5 +1,5 @@
 from django.db import models
-from core.models import Service, PlCoreBase, Slice, Instance, Tenant, TenantWithContainer, Node, Image, User, Flavor, Subscriber
+from core.models import Service, PlCoreBase, Slice, Instance, Tenant, TenantWithContainer, Node, Image, User, Flavor
 from core.models.plcorebase import StrippedCharField
 import os
 from django.db import models, transaction