Remove obsolete imports. #174

Job	Run time
Test (windows-latest, 3.6)	2m 58s
Test (windows-latest, 3.7)	1m 58s
Test (macos-latest, 3.6)	1m 18s
Test (windows-latest, 3.8)	2m 3s
Test (ubuntu-20.04, 3.6)	1m 8s
Test (macos-latest, 3.7)	1m 20s
Test (windows-latest, 3.9)	1m 42s
Test (ubuntu-20.04, 3.7)	32s
Test (macos-latest, 3.8)	52s
Test (windows-latest, 3.10)	1m 9s
Test (ubuntu-20.04, 3.8)	36s
Test (macos-latest, 3.9)	54s
Test (ubuntu-20.04, 3.9)	32s
Test (windows-latest, 3.11)	2m 11s
Test (macos-latest, 3.10)	1m 15s
Test (ubuntu-20.04, 3.10)	39s
Test (windows-latest, 3.12)	2m 31s
Test (macos-latest, 3.11)	1m 28s
Test (ubuntu-20.04, 3.11)	50s
Test (windows-latest, pypy-3.8)	1m 45s
Test (macos-latest, 3.12)	1m 21s
Test (ubuntu-20.04, 3.12)	1m 10s
Test (windows-latest, pypy-3.9)	2m 9s
Test (macos-latest, pypy-3.8)	47s
Test (ubuntu-20.04, pypy-3.8)	55s
Test (windows-latest, pypy-3.10)	1m 56s
Test (macos-latest, pypy-3.9)	58s
Test (ubuntu-20.04, pypy-3.9)	44s
Test (macos-latest, pypy-3.10)	49s
Test (ubuntu-20.04, pypy-3.10)	52s
Build source distribution	15s
Build wheels (3.6+) on ubuntu-20.04 for auto	5m 47s
Generate code coverage report	0s
Build wheels (3.6+) on windows-latest for auto	11m 8s
Build wheels (3.6+) on macos-latest for auto	4m 40s
Build wheels (3.6+) on ubuntu-20.04 for aarch64	16m 14s
Build wheels (3.6+) on macos-latest for arm64	3m 34s
	1h 21m 0s

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