www/py-django-timezone-field: Update to 4.0

• Also assign it to Django 2.2 (current LTS release) as Django 1.11 is End-of-Life since April 2020.

• Set the repo-copied port www/py-dj22-django-timezone-field as DEPRECATED because it's obsolete now. Don't set an expiration date yet as it's still used by net-mgmt/netbox and a few more Django 1.11 ports need to be assigned to Django 2.2 first.

• Also update the CONFLICTS_INSTALL entries as the repo-copied port py-dj21-django-timezone-field no longer exists in the Ports tree.

Changelog:

• Add support for Django 3.0 and Python 3.8
• Drop support for Django 1.11, 2.0, 2.1 and Python 2.7, 3.4

PR: 245309