Item page should render thumbnail only once

[bram-atmire]

Describe the bug

Prime "above the fold" screen real estate on item pages is being spent on rendering thumbnails, or the "no thumbnail" placeholder, twice.

To Reproduce

Steps to reproduce the behavior:

1. visit an item page on DSpace 10 angular that has an attached file

Expected behavior

We should only have one thumbnail. Even if there are multiple bitstreams, and the use case is "we should render thumbnails for all bitstreams", that would be an argument for dropping the rendering of the thumbnail on the left and only showing them in the bitstream rendering section.

[tdonohue]

NOTE: This behavior only appears if you have the new showDownloadLinkAsAttachment config set to true (the default value is false). See the description of that setting in the new "Layout settings" added in 10.0: https://wiki.lyrasis.org/spaces/DSDOC10x/pages/408944956/User+Interface+Configuration#UserInterfaceConfiguration-Layoutsettings

However, this is reproducible on demo.dspace.org and sandbox.dspace.org because we enable that configuration on those sites.