conf: Update for sphinx_rtd_theme 3.0.0

conf.py

@@ -186,16 +186,16 @@
 if on_rtd:
  os.system('git fetch --unshallow')
  os.system('pip freeze')
-else:
- import sphinx_rtd_theme
- html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
+#else:
+# import sphinx_rtd_theme
+# html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further. For a list of options available for each theme, see the
 # documentation.
 #html_theme_options = {}
 html_theme_options = {
- 'display_version': False,
+ #'display_version': False, # no longer needed in 3.0.0
  'navigation_depth': 5,
  'prev_next_buttons_location': None,
  #'canonical_url': 'https://scicomp.aalto.fi/'