Deleted Relationships may still appear selected in Lookup window in submission form

[tdonohue]

Describe the bug
When using Configurable Entities, if you add a related Entity and then delete the relationship, the deleted relationship still appears to exist in the Lookup window

To Reproduce
Steps to reproduce the behavior:

1. First, tested using the demo Entities data & Collections configured to match that data: https://github.com/DSpace-Labs/AIP-Files/releases/tag/demo-entities-data This same environment exists on https://api7.dspace.org
2. Create a new Submission in the "People" collection. This uses the Person form
3. In the "Publication" field, select an existing Publication to link to this Person. The Publication should appear back on the Submission form. Close the Lookup window.
4. On the Submission form, click the delete button next to that Publication. If you have Chrome DevTools open, you should see the DELETE request returns a 204. The Publication disappears from the submission form.
5. Click on the Lookup button again (opening the Lookup window). In that window the Publication will still appear as selected. (This is incorrect, as the Person should no longer be related to any Publication)

Expected behavior
After deleting the relationship, the Lookup window should no longer show any selected value.

Related work
Discovered when testing #1096, but it was not caused by that PR.

[tdonohue]

@artlowel : Assigning to you to review for possible inclusion in 7.0. I gave this low priority for now, as the feature works, but looks misleading to a user.