gnu: Remove python2-django-mailman3.

This package depends on Python 2 which is past end-of-life and not supported
by newer versions of Django.

* gnu/packages/mail.scm (python2-django-mailman3): Remove variable.
(python-django-mailman3)[properties]: Remove.

gnu/packages/mail.scm

@@ -3049,47 +3049,6 @@ installation on systems where resources are limited.  Its features include:
     (synopsis "Django library to help interaction with Mailman")
     (description
      "This package contains libraries and templates for Django-based interfaces
-interacting with Mailman.")
-    (properties `((python2-variant . ,(delay python2-django-mailman3))))
-    (license license:gpl3+)))
-
-;; This is the last version to support Python-2.
-(define-public python2-django-mailman3
-  (package
-    (name "python2-django-mailman3")
-    (version "1.1.0")
-    (source
-     (origin
-       (method url-fetch)
-       (uri (pypi-uri "django-mailman3" version))
-       (sha256
-        (base32
-         "1xjdkgfjwhgyrp5nxw65dcpcsr98ygj6856sp0bwkrmyxpd1xxk2"))))
-    (build-system python-build-system)
-    (arguments
-     `(#:phases
-       (modify-phases %standard-phases
-         (replace 'check
-           (lambda _
-             (invoke "django-admin"
-                     "test"
-                     "--settings=django_mailman3.tests.settings_test"
-                     "django_mailman3"))))
-       #:python ,python-2))
-    (inputs
-     `(("python2-django" ,python2-django)))
-    (propagated-inputs
-     `(("python2-requests" ,python2-requests)
-       ("python2-requests-oauthlib" ,python2-requests-oauthlib)
-       ("python2-openid" ,python2-openid)
-       ("python2-mailmanclient" ,python2-mailmanclient)
-       ("python2-django-allauth" ,python2-django-allauth)
-       ("python2-django-gravatar2" ,python2-django-gravatar2)
-       ("python2-pytz" ,python2-pytz)))
-    (home-page "https://gitlab.com/mailman/django-mailman3")
-    (synopsis "Django library for Mailman UIs")
-    (description
-     "Libraries and templates for Django-based interfaces
 interacting with Mailman.")
     (license license:gpl3+)))