Remove unused Buildkite scripts (part 1)

[dliappis]

Proposed commit message

This commit removes a number of Buildkite shell scripts that aren't used any more. It's a subset of #39188. Additionally removals will come in a future PR.

Related issues

• https://github.com/elastic/ingest-dev/issues/3219

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @dliappis? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Duration: 14 min 34 sec

❕ Flaky test report

No test was executed to be analysed.

🤖 GitHub comments

Expand to view the GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• /package : Generate the packages and run the E2E tests.

• /beats-tester : Run the installation tests with beats-tester.

• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)