Disable sphinxcontrib.napoleon, seems unused and isn't packaged in Debian

--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -24,8 +24,6 @@ from pyhamtools.version import __version
 # ones.
 extensions = [
     'sphinx.ext.autodoc',
-    'sphinx.ext.napoleon',
-    'sphinx_rtd_dark_mode',
 ]
 
 # Add any paths that contain templates here, relative to this directory.
@@ -97,7 +95,6 @@ pygments_style = 'sphinx'
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 # html_theme = 'default'
-html_theme = 'sphinx_rtd_theme'
 # html_theme = 'sphinx_material'
 
 # Theme options are theme-specific and customize the look and feel of a theme
