I would have left this as a comment on John Saunders' answer, but alas, my rep is not high enough :)
Vertical Selections
If you'd rather not be editing settings files, or you want to keep the automatic xml comment generation on typing "///", you could use vertical highlighting to select all the asterices and hit delete. Visual Studio, like Microsoft Office, gives you the ability to select a "column" of text: just hold alt and click-drag your selection across several lines.
It's possible you know this already, but it's still worth mentioning.
