[issue40443] Remove unused imports in the stdlib (April 2020 edition)

[Dong-hee Na]

Change by Dong-hee Na <donghee.na92 at gmail.com>:


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nosy: +corona10
nosy_count: 3.0 -> 4.0
pull_requests: +19617
pull_request: https://github.com/python/cpython/pull/20354

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40443>
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