www/py-django-taggit: Change RUN_DEPENDS
- Switch to Django 2.2 (current LTS release) because Django 1.11 is End-of-Life since April 2020.
- Bump PORTREVISION due changed dependencies.
- Also remove the repo-copied Django 2.1 port from CONFLICTS_INSTALL as it no longer exists in the Ports tree.
PR: 245309