Update flask stack

stack/flask.cfg

 # Stack for Flask microframework: http://flask.pocoo.org/
 [buildout]
 extends =
-  ../component/python-2.7/buildout.cfg
-  ../component/lxml-python/buildout.cfg
-
-# Use only quite well working sites.
-allow-hosts =
-  *.nexedi.org
-  *.python.org
-  *.sourceforge.net
-  dist.repoze.org
-  effbot.org
-  github.com
-  peak.telecommunity.com
-  psutil.googlecode.com
-  www.dabeaz.com
+  slapos.cfg
 
 parts =
-  eggs
-
-# Unzip, as Flask can have a lot of troubles with zipped eggs
-unzip = true
+  slapos-cookbook
+  flask-egg
 
-[eggs]
-python = python2.7
+[flask-egg]
 recipe = zc.recipe.egg
 eggs =
-  ${lxml-python:egg}
   Flask
-  slapos.cookbook
-
-[lxml-python]
-python = python2.7