[issue36624] cleanup the stdlib and tests with regard to sys.platform usage

[Tal Einat]

Change by Tal Einat <taleinat at gmail.com>:


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pull_requests: +13542
pull_request: https://github.com/python/cpython/pull/13648

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue36624>
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