delete custom workspaces?

I've just finished experimenting with the custom workspace feature and now my Workspace dropdown listbox (at the bottom of the Palettes frame) is filled not only with Basic and Advanced but several custom workspaces that I created only for the purpose of seeing how the feature works. After having fiddled with them for a while, now I want to get rid of them so they don't clutter the listbox. Unfortunately, I can't find a way to delete them. The manual doesn't say how on p. 178, nor does https://musescore.org/en/handbook/workspace.

Am I stuck with these useless workspaces?