Deleting a Newspaper fails to delete pages from its child issues

Originally brought up on a pull request,] about the apparently inaccurate warning when deleting a Newspaper object.

Deleting a Newspaper object via its Properties page warns the user that it this action will also delete all child Newspaper Issues, and Newspaper Pages belonging to those issues. This is not actually true. 

It appears that when you delete a Newspaper object, the pages of its child issues remain in the repository as orphans. This happens despite the progress bar claiming to be deleting the pages.

Using the Islandora Orphaned Objects module after deleting a newspaper reveals that all the pages remain in the repository.