Revert "Bump Sphinx to 5.3.0"

This reverts commit bb5a4703a7.

docs/conf.py

@@ -374,10 +374,6 @@ texinfo_documents = [
 # If true, do not generate a @detailmenu in the "Top" node's menu.
 #texinfo_no_detailmenu = False
 
-# If true, create table of contents entries for domain objects (e.g. functions,
-# classes, attributes, etc.).
-toc_object_entries=False
-
 def setup(app):
   if app.config.language == 'ja':
     app.config.intersphinx_mapping['py'] = ('https://docs.python.org/ja/3', None)