Merge pull request plone#1562 from plone/remove-duplicate-requirement

Remove duplicate requirement, sort secondary requirements

Author: stevepiercy

requirements.txt

@@ -15,6 +15,5 @@ sphinx-sitemap
 sphinx-togglebutton
 sphinxcontrib.httpdomain  # plone.restapi
 sphinxcontrib.httpexample  # plone.restapi
+sphinxcontrib-video
 sphinxext-opengraph
-sphinx-design
-sphinxcontrib-video