Retire django-developers and django-users mailing list

[thibaudcolas]

Following the forum thread (Proposal: retiring django-users and django-developers mailing lists), we can now move ahead with updating the website to remove or contextualize references to the django-developers and django-users mailing list. Corresponding Django ticket: Retire django-developers and django-users mailing list django#35908

Tasks

Here are relevant changes I think we should go ahead with:

• In the footer, remove the Django Users Mailing List item
• On the Community page, remove the "Mailing Lists" section
• On Download / How to get Django, replace "be sure to sign up for the django-users mailing list" with "be sure to sign up to the Django Forum"
• On the homepage, remove the "Stay in the loop" section