deprecate duplicate legacy dashboard

[salomekbg]

What does this PR do?

This is to deprecate the duplicate Legacy Kong dashboard.

Motivation

While checking the Kong dashboards to build an OpenMetrics version, I noticed that there seemed to be a duplicate OOTB dashboard for Legacy metrics. Got confirmation from Shri that this dashboard can be deprecated. Jira card

Additional Notes

Review checklist (to be filled by reviewers)

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• [ ] PR title must be written as a CHANGELOG entry (see why)
• [ ] Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• [ ] PR must have changelog/ and integration/ labels attached

[github-actions[bot]]

The validations job has failed; please review the Files changed tab for possible suggestions to resolve.

[github-actions[bot]]

The validations job has failed; please review the Files changed tab for possible suggestions to resolve.

[github-actions[bot]]

The validations job has failed; please review the Files changed tab for possible suggestions to resolve.

[yzhan289]

Closing in favor of https://github.com/DataDog/integrations-core/pull/12811