.ci: remove End-to-End Integration Tests stage

[axw]

What does this PR do?

Remove the end-to-end integration test stage. See elastic/apm-integration-testing#1523

Checklist

• This is something else
  • [ ] I have updated CHANGELOG.asciidoc

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Build stats

• Start Time: 2022-09-23T15:09:55.448+0000

• Duration: 60 min 43 sec

Test stats 🧪

Test	Results
Failed	0
Passed	3152
Skipped	36
Total	3188

💚 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.

• run benchmark tests : Run the benchmark tests.

• run jdk compatibility tests : Run the JDK Compatibility tests.

• run integration tests : Run the Agent Integration tests.

• run end-to-end tests : Run the APM-ITs.

• run windows tests : Build & tests on windows.

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