FIX: Rename delete_when_reminder_sent? bookmark method to avoid conflict with AR (PR #10333)

I added delete_when_reminder_sent to ignored_columns because it no longer exists and added a shortcut method delete_when_reminder_sent? to the Bookmark model. However I have been seeing some weird errors like:

Job exception: unknown attribute ‘delete_when_reminder_sent’ for Bookmark.

So I am very suspicious. I am just renaming the method to auto_delete_when_reminder_sent? to avoid any potential conflicts.