Blob storage management screen no longer shows if blob store is in use

The blob store management screen no longer shows if a blob store is in use by repositories, or other blob stores.

This is a regression.  Now the only way to tell if a blob store is in use is to try deleting it, which is a scary thing to do.

Expected: The blob store UI should clearly show if a blob store is being used so someone can know if it can be deleted.