github-action: delete opentelemetry workflow (backport #39559)

[mergify]

Details

⚠️ This PR was created by an automated tool. Please review the changes carefully. ⚠️

We want to delete the opentelemetry workflow.

Why

We now support Observing the CICD at large scale without the need to use a specialised
workflow.

Further details

https://ela.st/oblt-ci-cd-stats is the place to see the traces and logs for
all the GitHub actions.

There will be one service per GitHub repository, including the org name, and
one Transaction per Workflow.

If there are any questions, please reach out to the @elastic/observablt-ci

---

This is an automatic backport of pull request #39559 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 8b58916 has failed:

On branch mergify/bp/7.17/pr-39559
Your branch is up to date with 'origin/7.17'.

You are currently cherry-picking commit 8b58916153.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by them: .github/workflows/opentelemetry.yml

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[botelastic]

This pull request doesn't have a Team:<team> label.