You're correct that there is no "select all" option in the Archived Items page, and I'll certainly be passing along the feedback that it'd be helpful to have an option like that there.
Something important to note about that section is that once a contact is in Archived Items, they have already been removed from your account in terms of billing, sending, and reporting. It isn't necessary to completely delete them out of this page as well. It isn't going to have any affect on your account if you leave them in this state.
I hope this helps! Thanks again for reaching out and don't hesitate to follow-up if you have any other questions.