DeprecationWarning for USE_DEPRECATED_PYTZ, CSRF_COOKIE_MASKED, USE_L10N

[washeck]

When running tests on Django 4.2/Python 3.11 with -Wd switch, I am getting deprecation warning RemovedInDjango50Warning.

If I get it correctly, these should be added to ConfigurationBase.deprecated_settings. I can make a PR to address this but I'm not sure if just adding it there does not break things for users of older Django versions.

While looking at it, it seems to me that settings deprecated a long time ago (e.g. DEFAULT_CONTENT_TYPE) could be removed. Or do you plan to keep them on the list forever even though they are not present in Django's global_settings.py?