Deletes cron job runs that are older then the given timestamp.

def DeleteOldCronJobRuns(self, cutoff_timestamp, cursor=None):
    """Deletes cron job runs that are older then the given timestamp."""
    query = "DELETE FROM cron_job_runs WHERE write_time < FROM_UNIXTIME(%s)"
    cursor.execute(query,
                   [mysql_utils.RDFDatetimeToTimestamp(cutoff_timestamp)])