pythongh-104773: PEP 594: Remove the imghdr module

* Remove the Lib/test/imghdrdata/ directory.
* Copy 5 pictures (gif, png, ppm, pgm, xbm) from removed
  Lib/test/imghdrdata/ to a new Lib/test/tkinterdata/ directory.

Author: vstinner

Doc/library/imghdr.rst

@@ -97,8 +97,8 @@ Example:
 .. code-block:: pycon
 
    >>> import sndhdr
-   >>> imghdr.what('bass.wav')
+   >>> sndhdr.what('bass.wav')
    'wav'
-   >>> imghdr.whathdr('bass.wav')
+   >>> sndhdr.whathdr('bass.wav')
    'wav'
 

Doc/library/sndhdr.rst

@@ -16,7 +16,6 @@ backwards compatibility. They have been superseded by other modules.
    cgitb.rst
    chunk.rst
    crypt.rst
-   imghdr.rst
    mailcap.rst
    msilib.rst
    nis.rst

Doc/library/superseded.rst

@@ -102,6 +102,11 @@ Deprecated
 Removed
 =======
 
+* Remove the ``imghdr`` module, deprecated in Python 3.11: use the projects
+  `filetype <https://pypi.org/project/filetype/>`_,
+  `puremagic <https://pypi.org/project/puremagic/>`_,
+  or `python-magic <https://pypi.org/project/python-magic/>`_ instead.
+  (Contributed by Victor Stinner in :gh:`104773`.)
 
 
 Porting to Python 3.13