virtinst: do not depend on glanceclient

because its not a dependency and because its broken.

pkgs/applications/virtualization/virtinst/default.nix

···
   pythonPath = with python2Packages;
     [ setuptools eventlet greenlet gflags netaddr carrot routes
       PasteDeploy m2crypto ipy twisted
-      distutils_extra simplejson glanceclient cheetah lockfile httplib2
+      distutils_extra simplejson cheetah lockfile httplib2
       # !!! should libvirt be a build-time dependency?  Note that
       # libxml2Python is a dependency of libvirt.py.
       libvirt libxml2Python urlgrabber