[issue44498] add deprecation warnings for asynchat, asyncore and smtpd

[Irit Katriel]

Change by Irit Katriel <iritkatriel at gmail.com>:


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pull_requests: +25481
pull_request: https://github.com/python/cpython/pull/26905

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue44498>
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