gh-104773: PEP 594: Remove the sndhdr module

[vstinner]

Remove the Lib/test/sndhdrdata/ directory.

• Issue: PEP 594: Remove stdlib modules scheduled for deletion in Python 3.13 #104773

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📚 Documentation preview 📚: https://cpython-previews--104774.org.readthedocs.build/

[vstinner]

I ignored mentions of the sndhdr module in comments of the email module, Lib/email/mime/audio.py:

# Originally from the sndhdr module.
#
# There are others in sndhdr that don't have MIME types. :(
# Additional ones to be added to sndhdr? midi, mp3, realaudio, wma??
def _what(data):
    # Try to identify a sound file type.
    #
    # sndhdr.what() had a pretty cruddy interface, unfortunately.  This is why
    # we re-do it here.  It would be easier to reverse engineer the Unix 'file'
    # command and use the standard 'magic' file, as shipped with a modern Unix.
    hdr = data[:512]
    fakefile = BytesIO(hdr)
    for testfn in _rules:
        if res := testfn(hdr, fakefile):
            return res
    else:
        return None

[vstinner]

Fix the Docs CI: Warning: (...)/Doc/whatsnew/3.12.rst:819: WARNING: py:mod reference target not found: sndhdr.

[hugovk]

Please could you also update the refs in 3.11.rst?

For example with an exclamation mark:

* :pep:`594` led to the deprecations of the following modules
  slated for removal in Python 3.13:

  +---------------------+---------------------+---------------------+---------------------+---------------------+
  | :mod:`aifc`         | :mod:`chunk`        | :mod:`msilib`       | :mod:`pipes`        | :mod:`telnetlib`    |
  +---------------------+---------------------+---------------------+---------------------+---------------------+
  | :mod:`audioop`      | :mod:`crypt`        | :mod:`nis`          | :mod:`!sndhdr`      | :mod:`uu`           |
  +---------------------+---------------------+---------------------+---------------------+---------------------+
  | :mod:`cgi`          | :mod:`imghdr`       | :mod:`nntplib`      | :mod:`spwd`         | :mod:`xdrlib`       |
  +---------------------+---------------------+---------------------+---------------------+---------------------+
  | :mod:`cgitb`        | :mod:`mailcap`      | :mod:`ossaudiodev`  | :mod:`sunau`        |                     |
  +---------------------+---------------------+---------------------+---------------------+---------------------+

You could do them all in a single commit/PR, to avoid lots of conflicts later.

And:

diff --git a/Doc/whatsnew/3.5.rst b/Doc/whatsnew/3.5.rst
index 14b6425cea..a1b6e18950 100644
--- a/Doc/whatsnew/3.5.rst
+++ b/Doc/whatsnew/3.5.rst
@@ -1714,7 +1714,7 @@ support :rfc:`6531` (SMTPUTF8).
 sndhdr
 ------
 
-The :func:`~sndhdr.what` and :func:`~sndhdr.whathdr` functions  now return
+The ``what`` and ``whathdr`` functions now return
 a :func:`~collections.namedtuple`.  (Contributed by Claudiu Popa in
 :issue:`18615`.)

[vstinner]

I updated the doc: I added PEP 594 and replaced sndhdr with !sndhdr. I also rebased the PR on the main to retrieve recent test fixes (especially test_importlib).