Drop legacy iCal feed stuff

CHANGELOG.rst

aleksis/core/feeds.py

aleksis/core/frontend/routes.js

aleksis/core/migrations/0039_personal_ical_url.py

aleksis/core/migrations/0048_delete_personalicalurl.py

aleksis/core/models.py

aleksis/core/rules.py

aleksis/core/templates/core/ical/ical_create.html

aleksis/core/templates/core/ical/ical_edit.html

aleksis/core/templates/core/ical/ical_list.html

aleksis/core/urls.py

aleksis/core/views.py

pyproject.toml