docs: enable httpdomain sphinx extension

note: this was enabled only for swh-web, but it really needs to also be in
swh-docs, because we pull there docs from individual modules

docs/conf.py

@@ -5,5 +5,3 @@ os.environ.setdefault("DJANGO_SETTINGS_MODULE", "swh.web.settings.development")
 django.setup()
 
 from swh.docs.sphinx.conf import *  # NoQA
-
-extensions += ['sphinxcontrib.httpdomain'] # noqa