[docs] Removed sphinx.ext.githubpages

Let's move to readthedocs.org

docs/conf.py

@@ -29,9 +29,7 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = [
-    'sphinx.ext.githubpages',
-]
+extensions = []
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']