Fix lint warnings

.pylintrc

@@ -18,4 +18,5 @@ disable=
     redefined-outer-name,
     too-few-public-methods,
     too-many-ancestors,
+    too-many-arguments,
     unused-argument,

gregui/api/serializers/guest.py

-from django.db import transaction
 from rest_framework import serializers
 
 from greg.models import Identity, Person

gregui/tests/api/test_invitation.py

@@ -4,7 +4,7 @@ from rest_framework import status
 from rest_framework.reverse import reverse
 from rest_framework.test import APIClient
 
-from greg.models import Identity, InvitationLink, Person
+from greg.models import InvitationLink, Person
 
 
 @pytest.mark.django_db