Code review comment for lp:~dan-prince/glance/property_delete

Really clean patch Dan, great work.

I'm little worried by the semantics: a silent delete when a key isn't resubmitted. Though, there really aren't a whole lot of alternatives, and none that I can think of that don't involve some kind of magic, "DELETE ME IF YOU DETECT THIS" value.

So, this seems like the best approach available.