For my future benefit and for anyone who may be experiencing this, I hereby memorialize...
I don't know if this a bug or a feature, but I just re-learned that if you set a reference attribute as "Calculated", when you add a delete operation for reference instances, the delete button does not appear in the form. I thought that "Calculated" only pertained to updating (which is according the user guide), but that setting also prohibits deletion as well.
Calculated reference attribute instances cannot be deleted
Calculated reference attribute instances cannot be deleted
v8.1 on Windows 10 / MySQL 5.6 (local), v8.1 on Windows Server 2016 / MySQL 5.6 (server)