Remove message_extractors from setup.py since they currently prevent us from making a release (distutils raise an error).

setup.py

@@ -55,15 +55,6 @@ setup(name='plone.app.discussion',
               'plone.app.contenttypes[test]',
           ]
       },
-      message_extractors={
-          'src': [
-              ('**.py', 'lingua_python', None),
-              ('**.pt', 'lingua_xml', None),
-              ('**.cpt', 'lingua_xml', None),
-              ('**.zcml', 'lingua_xml', None),
-              ('**.xml', 'lingua_xml', None),
-          ],
-      },
       entry_points="""
       [z3c.autoinclude.plugin]
       target = plone