greg: fix various unused imports

All reported by pylint.

Fixes: GREG-16

greg/api/serializers/role.py

-from rest_framework import fields, serializers
+from rest_framework.serializers import ModelSerializer
 
 from greg.models import Role
 
 
-class RoleSerializer(serializers.ModelSerializer):
+class RoleSerializer(ModelSerializer):
     class Meta:
         model = Role
         fields = "__all__"

greg/api/views/role.py

-from django_filters import rest_framework as filters
-
 from rest_framework import viewsets
-from rest_framework.schemas.openapi import AutoSchema
 
 from greg.api.pagination import PrimaryKeyCursorPagination
 from greg.api.serializers.role import RoleSerializer

greg/apps.py

@@ -7,4 +7,4 @@ class GregAppConfig(AppConfig):
     verbose_name = _("Greg")
 
     def ready(self):
-        import greg.signals
+        import greg.signals  # pylint: disable=unused-import

greg/tests/test_api_person.py

 from django.contrib.auth import get_user_model
-from django.test import TestCase
-from django.utils.dateparse import parse_datetime
 from rest_framework import status
 from rest_framework.authtoken.models import Token
 from rest_framework.reverse import reverse
-from rest_framework.test import APIClient, APITestCase
+from rest_framework.test import (
+    APIClient,
+    APITestCase,
+)
 
-from greg.models import Person, PersonRole, Role
+from greg.models import Person
 
 
 class GregAPITestCase(APITestCase):

greg/urls.py

@@ -14,7 +14,6 @@ Including another URLconf
     2. Add a URL to urlpatterns:  path('blog/', include('blog.urls'))
 """
 from typing import List
-from django.contrib import admin
 from django.urls import path, include
 from django.urls.resolvers import URLResolver