[#45686429] Purge unamanged cron entries
[#45686429] Purge unamanged cron entries

Remove any entries in root's crontab that aren't managed by Puppet. This is
principally aimed at cleaning up old logster::crontab entries. It will also
catch any similar mistakes in the future.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet