code: def delete(self, pid, record, key):
          
          try:
              del record.files[str(key)]
              record.commit()
              db.session.commit()
              return make_response('', 204)
          except KeyError:
              abort(404, 'The specified object does not exist or has already '
                    'been deleted.')
docs: Handle DELETE deposit file.
  
          Permission required: `update_permission_factory`.
  
          :param pid: Pid object (from url).
          :param record: Record object resolved from the pid.
          :param key: Unique identifier for the file in the deposit.