translation: drop babel extractor definitions

babel extractors are now registered via python entry points,
so there is no need to declare babel extractors in babel configs.

This change is important to make translation work in Django 2.2.
django-babel does not work with Django 2.2 and looks unmaintained
for over two years. The horizon team is thinking to switch the extractor
to enmerkar (a fork of django-babel) to make extraction of translation
string work again near future. It is important to drop the extractor
definition to make the transition smooth.

Change-Id: I68b0eecd6b17be0e059fccdbced5784151c0e492

babel-django.cfg

@@ -1,6 +1,3 @@
-[extractors]
-django = django_babel.extract:extract_django
-
 [python: **.py]
 [django: **/templates/**.html]
 [django: **/templates/**.csv]

babel-djangojs.cfg

@@ -1,14 +1,2 @@
-[extractors]
-# We use a custom extractor to find translatable strings in AngularJS
-# templates. The extractor is included in horizon.utils for now.
-# See http://babel.pocoo.org/docs/messages/#referencing-extraction-methods for
-# details on how this works.
-angular = horizon.utils.babel_extract_angular:extract_angular
-
 [javascript: **.js]
-
-# We need to look into all static folders for HTML files.
-# The **/static ensures that we also search within
-# .../dashboards/XYZ/static which will ensure
-# that plugins are also translated.
 [angular: **/static/**.html]