[schema] BillingAddress.street2 is not required

schema.py

@@ -37,7 +37,7 @@ class has_shoppingitemtype(RelationDefinition):
 class BillingAddress(EntityType):
     organisation = String(required=True, maxsize=256)
     street = String(required=True, maxsize=256)
-    street2 = String(required=True, maxsize=256)
+    street2 = String(maxsize=256)
     postalcode = String(required=True, maxsize=256)
     city = String(required=True, maxsize=256)
     country = String(required=True, maxsize=256)