Adjust the listed items available in the media library so that there is only one clickable/focusable element per item

From @cboyden after testing 🐛 Ensure that when the Media Library disables media items so that they cannot be selected, that they are also disabled for screenreader access Needs work

Lucy and I reviewed the patch. The disabled elements are still announced as "clickable," but, clicking on the "clickable" elements no longer does anything. The NVDA user is no longer able to select more items that are allowed by the field.

For each library item, there are two clickable elements that are available when using NVDA's arrow navigation. Either one works to select the item. It would make for better screenreader usability if there were only one actionable element per media item.

The original ticket can be referenced for more context, and this interaction can be viewed on the video recording of the September 29, 2019 walkthrough of Media Library starting at around minute 6:30 and continuing to minute 9:45.

Additional note: addressing this will also improve the experience for keyboard-only users (in addition to screenreader users), as it will reduce the number of tabs required to interact with the interface.