How do I remove this? I don't use that feature at *all* and frankly, having it there annoys me. Thanks.

Do you want to remove the entire treebar or just the notify nicks?

To remove the entire treebar open the View menu and deselect Treebar.

To remove the nicknames on your notify list from the treebar right-click an empty are of the treebar, go to Notify List and select "None"

Durr. I feel dumb now. Thanks!