Removing the last few references to hg.dwscoalition.org

[kaberett]

• Template:Changeset needs updating (as in, the template itself, not just the page)
  
• Production Setup: Webserver badly needs updating, not just because of the references to Mercurial
  
• Dev Tools needs updating by someone who knows what's happening (i.e. not me)
  
• Summer of Code 2010: leave as historical document, or update in case we ever want to reuse the text?