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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def DeleteOldRuns(self, job, cutoff_timestamp=None, token=None):
 """Deletes flows initiated by the job that are older than specified."""

    if cutoff_timestamp is None:
      raise ValueError("cutoff_timestamp can't be None")

    child_flows = list(job.ListChildren(age=cutoff_timestamp))
    with queue_manager.QueueManager(token=token) as queuemanager:
      queuemanager.MultiDestroyFlowStates(child_flows)

    aff4.FACTORY.MultiDelete(child_flows, token=token)
    return len(child_flows)