Remove d2to1

d2to1 is deprecated (see https://github.com/embray/d2to1) and no longer
works with setuptools >= 68.0.0, so this project's wheel can no longer
be built:

  Traceback (most recent call last):
    [...]
    File "/tmp/pip-build-env-mt7emmq3/overlay/lib/python3.12/site-packages/setuptools/dist.py", line 674, in _finalize_setup_keywords
      ep.load()(self, ep.name, value)
    File "/tmp/pip-build-env-mt7emmq3/normal/lib/python3.12/site-packages/d2to1/core.py", line 30, in d2to1
      from setuptools.dist import _get_unpatched
  ImportError: cannot import name '_get_unpatched' from 'setuptools.dist' (/tmp/pip-build-env-mt7emmq3/overlay/lib/python3.12/site-packages/setuptools/dist.py). Did you mean: 'get_unpatched'?

Port to plain modern setuptools.

celery_haystack/__init__.py

 __version__ = '2.0'
-
-
-def version_hook(config):
-    config['metadata']['version'] = __version__

setup.cfg

-[global]
-setup-hooks =
-    celery_haystack.version_hook
-
 [metadata]
 name = celery-haystack-ng
+version = attr: celery_haystack.__version__
 author = Dominik George
-author-email = dominik.george@teckids.org
-summary = An app for integrating Celery with Haystack
-description-file = README.rst
-home-page = http://celery-haystack-ng.rtfd.org/
-project-url =
-    https://edugit.org/AlekSIS/libs/celery-haystack-ng
-classifier =
+author_email = dominik.george@teckids.org
+description = An app for integrating Celery with Haystack
+long_description = file: README.rst
+url = http://celery-haystack-ng.rtfd.org/
+project_urls =
+    Code=https://edugit.org/AlekSIS/libs/celery-haystack-ng
+classifiers =
     Development Status :: 4 - Beta
     Environment :: Web Environment
     Framework :: Django
@@ -22,20 +19,11 @@ classifier =
     Topic :: Utilities
 
 [options]
+packages = find:
 install_requires =
     django-appconf>=0.4.1
     django-haystack>=2.0
     celery>=4.0
-
-[files]
-packages =
-    celery_haystack
-    celery_haystack.tests
-extra_files =
-    README.rst
-    AUTHORS
-
-[backwards_compat]
 zip_safe = False
 
 [wheel]

setup.py

 #!/usr/bin/env python
 from setuptools import setup
 
-setup(setup_requires=['d2to1'], d2to1=True)
+setup()