Remove python 2 support

[basepi]

As discussed with @sethmlarson, the python client is removing support for python 2 in 8.0, so ecs-logging-python can follow suit. 🎉

We'll want to move from comment-based type checking to python 3 type hints but I think that should be a separate PR.

[apmmachine]

💚 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

• Start Time: 2022-01-11T18:10:21.308+0000

• Duration: 9 min 56 sec

• Commit: b174939

Test stats 🧪

Test	Results
Failed	0
Passed	269
Skipped	0
Total	269

🤖 GitHub comments

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

• /test : Re-trigger the build.

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

[sethmlarson]

Looks good, only one blocking comment from me. A non-blocking comment: have you tried pyupgrade --py36-plus and flynt on the codebase? Might change some string formatting into f-strings and other modernizations.

[basepi]

Ran flynt/pyupgrade and fixed up a few things