Notifications are not actually deleted in some circumstances of bulk cleanup

Problem/Motivation

There is an error in \Drupal\activity_creator\ActivityNotifications::deleteNotificationsByIds. On line 260 of ActivityNotifications.php the line ->condition('aid', $activity_ids) is used, where $activity_ids is an array. However, the default comparison operator for condition is = which causes issues in the query, resulting in unremoved activities.

Steps to reproduce

1. Create a new user
2. Create a lot of content with the user (some events, posts, groups)
3. Ensure cron has run
4. Delete the user through the command line using drush php-eval '\Drupal\user\Entity\User::load(10)->delete();' replacing 10 with the ID of your user
5. You should see SQL errors on the console regarding the removal

Proposed resolution

• Ensure the correct operator is used in condition, in this case add "IN" as third argument. Similar to what's done on line 196 of the same file
• Create an update hook that cleans up any notifications for whom the user or associated entity no longer exists.

Remaining tasks

1. Reproduce
2. Create fix
   • Ensure the correct operator is used
   • Create an update hook
3. Test
4. Write release notes
5. Review
6. Commit

User interface changes

None expected

API changes

None expected

Data model changes

None expected