Clean up python2 related code crafts

[auvipy]

Fixes #

Description of the Change

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #974 (f78901b) into master (50841f7) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #974   +/-   ##
=======================================
  Coverage   96.82%   96.82%           
=======================================
  Files          65       65           
  Lines        3904     3904           
=======================================
  Hits         3780     3780           
  Misses        124      124           

Impacted Files	Coverage Δ
rest_framework_json_api/relations.py	88.46% <100.00%> (ø)
rest_framework_json_api/renderers.py	90.15% <100.00%> (ø)
rest_framework_json_api/settings.py	100.00% <100.00%> (ø)
example/serializers.py	89.14% <0.00%> (ø)

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[sliverc]

Thanks for this clean up task. Really appreciated. Could you please run black . and push again? Then it will be ready for merging.

[auvipy]

OK sure

[auvipy]

pushed new changes

[sliverc]

Thanks for your contribution. LGTM.

[auvipy]

would be happy to help. thanks for this cool project.