Sorry for the necro, but I came here looking for the answer too. To remove accidental multiple moons, and the mod itself if desired:

Turn on development mode -> At the top of the screen click "Open Debug Actions Menu" -> Under "Map Management" Click "Destroy Map" -> Select each moon map (Unless your base is on a moon, it is probably not any marked as player base -> Save without viewing world map and restart game.

Further to delete mod safely from the game, delete all moon maps without viewing the world map, save, go to main menu and disable the mod, and restart without the Rimnaut mod, this should delete the moon and NEOs without damaging the save file.