How to delete or unshare a USB drive?

I have a USB drive that I had initially intended to use as a backup for my MBLD, however, I inadvertently marked it as a share. I don’t want to back it up to itself or to my other network backup drive (I’m a firm believer in redundancy when it comes to my data).

How do I un-share this USB drive so that I can use it as a secondary backup for the MBLD? There is no delete icon for this drive in the Share List.

After creating a backup on a network drive I realized that the USB drive isn’t backed up - just the MBLD.