fix(downloads): delete files, attachments and screenshots after the dialog
Deleting a file, an additional file or a screenshot is a POST form that asks in the dialog of the page and sits behind RequireConfirmationMiddleware: POST /downloads/delete-file/{id}, /downloads/additional-files/{id}/delete and /downloads/edit-screen/{id}/delete. The separate confirmation pages and the session delete_token are gone, a screenshot used to be deleted with no question at all, and an additional file is only reached through the file it belongs to.