docs: simplify conf.py and fix compatibility with upcoming Sphinx 6.0

Change-Id: I970c5691cb4b1879854023a3747c2bf63189c128
diff --git a/docs/named_data_theme/layout.html b/docs/named_data_theme/layout.html
index 78b6477..aa25686 100644
--- a/docs/named_data_theme/layout.html
+++ b/docs/named_data_theme/layout.html
@@ -12,7 +12,7 @@
         <div class="row">
              <div class="three columns">
                   <div id="logo">
-                        <a href="http://named-data.net" title="A Future Internet Architecture"><img src="http://named-data.net/wp-content/uploads/cropped-20130722_Logo2.png" alt="" /></a>
+                        <a href="https://named-data.net" title="A Future Internet Architecture"><img src="https://named-data.net/wp-content/uploads/cropped-20130722_Logo2.png" alt="" /></a>
                   </div><!--logo end-->
              </div>
 
@@ -41,7 +41,6 @@
           <h3>{{ _('Developer documentation') }}</h3>
           <ul>
             <li class="toctree-l1"><a class="reference internal" href="doxygen/annotated.html">API documentation (doxygen)</a></li>
-            <li class="toctree-l1"><a class="reference internal" href="code-style.html">ndn-cxx Code Style and Coding Guidelines</a></li>
           </ul>
           {%- endblock %}
 
@@ -75,7 +74,7 @@
         <div class="row">
             <div class="twelve columns">
 
-                <div id="copyright">This research is partially supported by NSF (Award <a href="http://www.nsf.gov/awardsearch/showAward?AWD_ID=1040868" target="_blank>">CNS-1040868</a>)<br/><br/><a rel="license" href="http://creativecommons.org/licenses/by/3.0/deed.en_US" target="_blank">Creative Commons Attribution 3.0 Unported License</a> except where noted.</div>
+                <div id="copyright">This research is partially supported by NSF (Award <a href="https://www.nsf.gov/awardsearch/showAward?AWD_ID=1040868" target="_blank>">CNS-1040868</a>)<br/><br/><a rel="license" href="https://creativecommons.org/licenses/by/3.0/deed.en_US" target="_blank">Creative Commons Attribution 3.0 Unported License</a> except where noted.</div>
 
             </div>
         </div>