When a category is removed from `auto_watch_category` we are removing
CategoryUser. However, there are still TopicUser with notification level
set to `watching` which was inherited from Category.
We should move them back to `regular` unless they were modified by a user.
Co-authored-by: Mark VanLandingham <markvanlan@gmail.com>
Co-authored-by: Robin Ward <robin.ward@gmail.com>
Co-authored-by: Mark VanLandingham <markvanlan@gmail.com>