Split screen divider stuck on Desktop, not actually dividing any windows, distracting - how to remove?

How can the split screen divider be removed, please? When not using a Desktop workspace/area, I can see the vertical divider over the Desktop, but this isn't serving any purpose and is therefore distracting. See screenshot: MacBook Air 11" 2015, 1366 x 768 screen, 8Gb RAM, 2.2 Ghz i7, 500Gb SSD, macOS mojave 10.14.2 Additional screenshots: Notifications pop-up goes over the split divider (Answering question in comments from @bmike ) On opening e.g. Chrome, this goes on top of the divider, but the divider can then be dragged over the window as shown.