docs: Remove intersphinx mapping for python-mock

python-mock is now part of the Python standard library (available as
unittest.mock in Python 3.3 onwards) and all documentation on
voidspace.org.uk is removed.

doc/conf.py

@@ -343,10 +343,6 @@ def check_object_path(key, url, path):
         return {key: (url, None)}
 
 intersphinx_mapping = {}
-intersphinx_mapping.update(\
-    check_object_path('mock',
-                      'http://www.voidspace.org.uk/python/mock',
-                      '/usr/share/doc/python-mock-doc/html/objects.inv'))
 intersphinx_mapping.update(\
     check_object_path('cherrypy',
                       'http://docs.cherrypy.org/stable',