doc/conf: remove some rtd_theme options

These options are not essential and they are only supported with newer
versions of the theme, which are unavailable in older distributions.

doc/conf.py

@@ -61,8 +61,6 @@ html_theme_options = {
     # Toc options
     'collapse_navigation': False,
     'sticky_navigation': True,
-    'navigation_depth': 3,
-    'includehidden': False,
 }
 html_logo = '_static/logo-negativ.svg'