removed core/extras ref from module pages

fixes #20647

docs/docsite/_themes/srtd/footer.html

@@ -30,6 +30,6 @@
   {%- endif %}
   </p>
 <p>
-Ansible docs are generated from <a href="https://github.com/ansible/ansible">GitHub sources</A> using <A HREF="http://sphinx-doc.org/">Sphinx</A> using a theme provided by <a href="http://readthedocs.org">Read the Docs</a>. {% if pagename.endswith("_module") %}. Module documentation is not edited directly, but is generated from the source code for the modules.  To submit an update to module docs, edit the 'DOCUMENTATION' metadata in the <A HREF="https://github.com/ansible/ansible-modules-core">core</A> and <A HREF="https://github.com/ansible/ansible-modules-extras">extras</A> modules source repositories. {% endif %}
+Ansible docs are generated from <a href="https://github.com/ansible/ansible">GitHub sources</A> using <A HREF="http://sphinx-doc.org/">Sphinx</A> using a theme provided by <a href="http://readthedocs.org">Read the Docs</a>. {% if pagename.endswith("_module") %}. Module documentation is not edited directly, but is generated from the source code for the modules. To submit an update to module docs, edit the 'DOCUMENTATION' metadata in the module itself.{% endif %}
 </p>
 </footer>