http://community.shavlik.com/docs/DOC-23055 outlines a way to remove snapshots by faking another patch job shortly after the real one. What I don't understand however, is in step 4, it says "You need to set this to take pre-deployment snapshots as well". Would not the fake job create another snapshot after removing the previous one?
Currently - Yes it does. It will remove the old snapshots, but it will only do this at the time that a new snapshot is created.
I'm guessing you (like many others) would like to see this changed. If you haven't already, please take the time to submit a feature/change request at http://shavlik.featureidea.com so that our product management team continues to see any requests around these features.