There is no mod that does so to my knowledge, but it is easy enough to mod them out of SE4. Open up the SystemTypes.txt file and remove all entries that are planets and have the placement type of "same as X." That is what makes them moons. Of course, I strongly urge that you do not modify your stock data and instead create a mod folder to modify.
Edit:
Beat me by a second or two.
[ January 27, 2004, 02:06: Message edited by: Imperator Fyron ]