[8.13](backport #39534) Remove unused env vars from pipelines

[mergify]

Proposed commit message

This PR performs some cleanup on some environment variables used in the dockerlogbeat and osquerybeat pipelines.

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This is an automatic backport of pull request #39534 done by Mergify.

[botelastic]

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

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b mergify/bp/8.13/pr-39534 upstream/mergify/bp/8.13/pr-39534
git merge upstream/8.13
git push upstream mergify/bp/8.13/pr-39534

[alexsapran]

closing, since the GH PR view is saying that there are conflicts, which I cannot see when checking out locally.

[dliappis]

LGTM