Remove legacy manage.py

Use an installed django-admin script instead, e.g. `poetry run
django-adimn …`

manage.py

-#!/usr/bin/env python3
-import os
-import sys
-
-if __name__ == "__main__":
-    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "aleksis.core.settings")
-    try:
-        from django.core.management import execute_from_command_line
-    except ImportError as exc:
-        raise ImportError(
-            "Couldn't import Django. Are you sure it's installed and "
-            "available on your PYTHONPATH environment variable? Did you "
-            "forget to activate a virtual environment?"
-        ) from exc
-    execute_from_command_line(sys.argv)

pyproject.toml

@@ -5,7 +5,7 @@ packages = [
     { include = "aleksis" }
 ]
 readme = "README.rst"
-include = ["CHANGELOG.rst", "LICENCE.rst", "manage.py", "docs/*", "docs/**/*", "tox.ini"]
+include = ["CHANGELOG.rst", "LICENCE.rst", "docs/*", "docs/**/*", "tox.ini"]
 
 description = "AlekSIS (School Information System) — Core"
 authors = ["Dominik George <dominik.george@teckids.org>", "Julian Leucker <leuckeju@katharineum.de>", "mirabilos <thorsten.glaser@teckids.org>", "Frank Poetzsch-Heffter <p-h@katharineum.de>", "Tom Teichler <tom.teichler@teckids.org>", "Jonathan Weth <wethjo@katharineum.de>", "Hangzhi Yu <yuha@katharineum.de>"]