Thumbnails break display of modal when deleting an Entity relationship

[tdonohue]

Describe the bug
When deleting an Entity relationship, you are shown a popup/modal window which asks "Select the items for which you want to save the virtual metadata as real metadata". The display in this window is currently broken by improper thumbnail display. Here's a screenshot example:

To Reproduce
Steps to reproduce the behavior:

1. Login as an Admin
2. Edit an Entity which has existing relationships. For example, edit "Simmons, Cameron" or one of their Publications
3. On the "Relationships" tab, attempt to delete a relationship. You'll see a popup modal like the above screenshot.

Expected behavior
Either the thumbnails should be displayed properly in the popup, or alternatively no thumbnails should be displayed in this popup (as they are likely not necessary).

Related work
Somewhat similar to #1855, except for this popup window. However, this bug ticket might be fixed by simple CSS or removing thumbnails entirely from this display.

[tdonohue]

@artlowel or @ybnd : Any chance one of you could look at this tomorrow during your day? This might be a tiny CSS issue, or I'm also OK with just disabling thumbnails in this popup.

[mspalti]

@tdonohue, I should be able to find a fix today.

[tdonohue]

Thanks @mspalti : If you can find a fix, I'd be glad to test it as soon as the PR is ready to go.