... I believe the file you want to edit there, however, is the defaults.list file.
Not true in my case. I do not have any icons on my desktop, other than the default "My Documents" icon, so the only .desktop files I had in /home/rg/.local/share/applications/ were files for the duplicate menu items (right-click, "Open with ...)". Removing those .desktop files alone removed the duplicate menu items. Afterwards, I also found references to those .desktop files in defaults.list and mimeinfo.cache, and those references to the unwanted .desktop files were edited-out manually. The unwanted .desktop files were named "leafpad-user-created ...", etc., as best as I can remember.
I saw this solution posted at:http://forum.lxde.org
where the forum moderator replied to a message.