Remove the Github Pages Sphinx extension

readthedocs.org has an older version of Sphinx that doesn't include this
extension by default, and we are not going to use it, so this turns it
off.

Signed-off-by: Jeremy Cline <jeremy@jcline.org>

docs/conf.py

@@ -34,7 +34,6 @@
     'sphinx.ext.autodoc',
     'sphinx.ext.doctest',
     'sphinx.ext.viewcode',
-    'sphinx.ext.githubpages',
 ]
 
 # Add any paths that contain templates here, relative to this directory.