remove usage of compat helpers for Python 2 compatibility

[beniwohli]

What does this pull request do?

Removes all usage of Python 2-specific usage of the compat module.

First commit is only the elasticapm module, second commit is the test suite.

Related issues

closes #ISSUE

[ghost]

💚 Build Succeeded

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Build stats

• Start Time: 2022-02-16T08:24:03.883+0000

• Duration: 26 min 21 sec

Test stats 🧪

Test	Results
Failed	0
Passed	4818
Skipped	2918
Total	7736

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

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

• /test : Re-trigger the build.

• /test linters : Run the Python linters only.

• /test full : Run the full matrix of tests.

• /test benchmark : Run the APM Agent Python benchmarks tests.

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

[beniwohli]

/test full

[beniwohli]

/test full

[basepi]

Yay! 🎉