Stop sending service domain to the API

The API doesn’t look at it, and the rest of the admin code isn’t calling
the method with this argument any more.

app/notify_client/service_api_client.py

@@ -13,7 +13,6 @@ class ServiceAPIClient(NotifyAdminAPIClient):
         restricted,
         user_id,
         email_from,
-        service_domain,
     ):
         """
         Create a service and return the json.
@@ -26,7 +25,6 @@ class ServiceAPIClient(NotifyAdminAPIClient):
             "user_id": user_id,
             "restricted": restricted,
             "email_from": email_from,
-            "service_domain": service_domain
         }
         data = _attach_current_user(data)
         return self.post("/service", data)['data']['id']