fixing migration and allowing valid rollback on typical migrations

helpdesk/migrations/0010_remove_queuemembership.py

@@ -19,11 +19,6 @@ class Migration(migrations.Migration):
             model_name='queuemembership',
             name='user',
         ),
-        migrations.AddField(
-            model_name='queue',
-            name='permission_name',
-            field=models.CharField(help_text='Name used in the django.contrib.auth permission system', max_length=50, null=True, verbose_name='Django auth permission name', blank=True),
-        ),
         migrations.DeleteModel(
             name='QueueMembership',
         ),