Remove all deprecated code

[sliverc]

Fixes #662

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 #688 into master will decrease coverage by 0.15%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #688      +/-   ##
==========================================
- Coverage   96.12%   95.96%   -0.16%     
==========================================
  Files          56       54       -2     
  Lines        2866     2728     -138     
==========================================
- Hits         2755     2618     -137     
+ Misses        111      110       -1

Impacted Files	Coverage Δ
example/tests/test_parsers.py	100% <ø> (ø)	⬆️
rest_framework_json_api/pagination.py	92.68% <ø> (-2.4%)	⬇️
example/tests/unit/test_renderers.py	100% <ø> (ø)	⬆️
example/tests/unit/test_default_drf_serializers.py	100% <ø> (ø)	⬆️
example/tests/unit/test_utils.py	100% <ø> (ø)	⬆️
rest_framework_json_api/settings.py	100% <ø> (ø)	⬆️
example/tests/unit/test_pagination.py	100% <ø> (ø)	⬆️
rest_framework_json_api/parsers.py	97.1% <100%> (ø)	⬆️
rest_framework_json_api/renderers.py	86.79% <100%> (ø)	⬆️
example/api/resources/identity.py	100% <100%> (ø)	⬆️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

Merging #688 into master will decrease coverage by 0.15%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #688      +/-   ##
==========================================
- Coverage   96.12%   95.96%   -0.16%     
==========================================
  Files          56       54       -2     
  Lines        2866     2728     -138     
==========================================
- Hits         2755     2618     -137     
+ Misses        111      110       -1

Impacted Files	Coverage Δ
example/tests/test_parsers.py	100% <ø> (ø)	⬆️
rest_framework_json_api/pagination.py	92.68% <ø> (-2.4%)	⬇️
example/tests/unit/test_renderers.py	100% <ø> (ø)	⬆️
example/tests/unit/test_default_drf_serializers.py	100% <ø> (ø)	⬆️
example/tests/unit/test_utils.py	100% <ø> (ø)	⬆️
rest_framework_json_api/settings.py	100% <ø> (ø)	⬆️
example/tests/unit/test_pagination.py	100% <ø> (ø)	⬆️
rest_framework_json_api/parsers.py	97.1% <100%> (ø)	⬆️
rest_framework_json_api/renderers.py	86.79% <100%> (ø)	⬆️
example/api/resources/identity.py	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7efd877...4de86b4. Read the comment docs.

[n2ygk]

@sliverc Thanks for taking out the trash!