Remove the internal group ID setting

While working on #1716 (closed), I found that we still had a internal_group_id configuration option, which was left here to run a migration that we have since deleted in !2007 (merged).

arkindex/documents/management/commands/build_fixtures.py

@@ -49,7 +49,7 @@ class Command(BaseCommand):
         img5 = Image.objects.create(path="img5", width=1000, height=1000, server=imgsrv)
         img6 = Image.objects.create(path="img6", width=1000, height=1000, server=imgsrv)
 
-        # Create an admin, an internal and a normal user
+        # Create an admin and a normal user
         superuser = User.objects.create_superuser("root@root.fr", "Pa$$w0rd", display_name="Admin")
         superuser.verified_email = True
         superuser.save()