$ sudo gedit /etc/xdg/user-dirs.defaults
To remove folders, comment them out with the # symbol, you can also add files to the list.
~/.config/user-dirs.dirs changes the sidebar folder for the current session, but on boot it gets rebuild from /etc/xdg/user-dirs.defaults, that's why you have to edit both.
I did not yet find a way to choose the order of the folders in the sidebar, I anyone know how to do this, please let me know.
Thanks, this is helpful. To see the change, I had to reload the Gnome desktop (Alt-F2 and then r). I did notice that it moves the commented out folder to your "bookmarks" which you can then remove.
Edit:
I found that this did not persist after a reboot. Thoughts on how to make it "stick"?
I facepalmed... I am sorry Hanne, I have been busy with a lot of other things... That is where my edits are made. I should have remembered that and mentioned it earlier... It really did not occur to me. My only excuse is that I blame my brain.