How can I delete orphaned Product Displays?
Perhaps a PHP script that mimics creation of that View list and then utilizes a node_delete_multiple().  Granted, you will want to test this out very carefully before actually using a method like this.  

That said, an Entity Field Query coupled with a node_delete_multiple() may be what you're looking for.  Again, test very well, look at the DB after a test run, see that everything you want deleted is.