Remove Grafana attribute and deprecation messages

What does this MR do?

Remove Grafana attribute and deprecation messages

- Grafana was removed in GitLab 16.3. This removes the deprecation
  messages and the attribute that was left behind to enable those
  messages to fire without error.

Closes https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/8200

Changelog: removed

Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

Related issues

Closes Remove Grafana attribute and deprecation messages (#8200 - closed) • Robert Marshall • 17.1

Checklist

See Definition of done.

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Required

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Expected (please provide an explanation if not completing)

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