Merge branch 'doc-remove-updated-at-audit-events' into 'master'

Remove stale updated_at field

See merge request gitlab-org/gitlab!25324

doc/administration/audit_events.md

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-last_updated: 2019-09-16
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 # Audit Events **(STARTER)**
 
 GitLab offers a way to view the changes made within the GitLab server for owners and administrators on a [paid plan][ee].