Remove dumppickedversions, included w/buildout2

We can go one of two ways here: remove dumppickedversions or pin zc.buildout to 1.7.x. I don't have a strong preference, but since I'd like to see Buildout 2 get some use I'm going to remove dumppickedversions for now (AFAICT devstart does not currently specify a version of zc.buildout, and therefore it gets the latest).