Remove BK PR Bot trigger for packetbeat

[dliappis]

Proposed commit message

In preparation for the migration to a static pipeline for packetbeat, this commit removes the Buildkite PR Bot trigger.

Related issues

• elastic/ingest-dev#3072

[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

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Build stats

• Start Time: 2024-04-19T14:00:28.016+0000

• Duration: 14 min 12 sec

Test stats 🧪

Test	Results
Failed	0
Passed	3
Skipped	0
Total	3

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

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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!)