Remove asyncore and asyncio from CPython code

[arhadthedev]

PEP 594 removes asynchat and asyncore modules from Python 3.12 onwards. This issue tracks what needs to be done to implement this part of the PEP.

Note that some preparation entries below require not-yet-existing asyncio.StreamWriter.shutdown_tls(). The method, in its turn, needs asyncio infrastructural changes described in python#92679.

The list:

• Preparation (found with asynchat|asyncore search in file content)
  • smtpd module
  • [x] Doc\library\smtpd.rst
  • [x] Lib\smtpd.py
  • [ ] Lib\test\libregrtest\save_env.py
  • [ ] Lib\test\test_ftplib.py
  • [ ] Lib\test\test_logging.py
  • [ ] Lib\test\test_poplib.py
  • [x] Lib\test\test_smtpd.py
    • gh-5
  • [ ] Lib\test\test_smtplib.py
  • [ ] Lib\test\test_ssl.py
• [ ] Final removal from test
  • branch: https://github.com/arhadthedev/cpython/tree/remove-asynchat-asyncore
• [x] Add NEWS entry
• [x] Advertise the removal in What's New

[arhadthedev]

Closed in favor of CPython issue 93243.