[Task] Remove django-newsletter #335
Description
Describe the task
The django-newsletter app has been incorporated into this project for a couple of years, and worked well. However, some issues with markdown media storage, paired with a lot of spammers creating thousands of fake subscriptions for random people led me to look elsewhere. These weren't issues with django-newsletter really, they are just complicated that would have taken more time to address, so I decided to migrate to a new platform, micro.blog/oldinsurancemaps, which provides a newsletter functionality, and also allows me to combine the other blog website I had made separately directly into a single feed.
All of that has been handled, so this ticket is now to remove the now-unused django-newsletter app from this code base.
Completion criteria
Remove all references to newsletter.models and all page views that had been made to display the archive list.
Additional context
I have already created dozens of redirects (using Django's built-in redirect app) to handle all of the old "permalinks" that will no longer lead to newsletter archive posts on this site.