I found this
. Seems to be that the "Recently used" choices are generated from a file called .recently-used.xbel
(note the preceding dot, indicating that it's a hidden file.) On my machine, I think it's located at /home/mark/.local/share/recently-used.xbel (so, in a hidden directory rather than a hidden file).
The link I gave seems to indicate that eliminating this file and placing a directory with the same name as the file in the same location will prevent the file from being created, thus ending the compilation of "Recently used" choices from appearing (see the "EDIT" in the link
). I don't know if this will work, but it could be something to try.