def backwards(self, orm):
        for t in orm['sts.Transition'].objects.filter(end_time__isnull=False):
            t.duration = (t.end_time - t.start_time).seconds
            t.save()
Removes a header with the passed name.
dataset/ETHPy150Open chop-dbhi/django-sts/sts/migrations/0003_convert_duration_to_milliseconds.py/Migration.backwards--crossover with--dataset/ETHPy150Open armet/python-armet/armet/http/response.py/Headers.__delitem__