remove extension that is no longer needed

.website_src/conf.py

@@ -29,7 +29,7 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = [ 'sphinx.ext.mathjax', 'sphinx_toolbox.collapse', 'sphinx_copybutton', 'sphinx_mdinclude', 'myst_nb' ]
+extensions = [ 'sphinx.ext.mathjax', 'sphinx_toolbox.collapse', 'sphinx_copybutton', 'myst_nb' ]
 
 
 # Add any paths that contain templates here, relative to this directory.