clean some leftover from previous refactor #275

Job	Run time
Tox test (py38)	2m 38s
Tox test (py39)	2m 35s
Tests on paywalled platforms	0s
Tests on other platforms (windows-2019, 3.10)	3m 9s
Tox test (py310)	2m 41s
Tests on other platforms (windows-2022, 3.11)	2m 49s
Tox test (py311)	2m 34s
Tests on other platforms (windows-2022, 3.12)	3m 26s
Tox test (py312-cover)	5m 15s
Tests on other platforms (macos-12, 3.11)	2m 54s
Tox test (docs, graphviz)	1m 51s
Tests on other platforms (macos-13, 3.12)	2m 58s
PyPI packaging	0s
Docker image	0s
	32m 50s

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