small sphinx tweaks. require sphinx 5.2 or later.

doc/utils/sphinx-config/conf.py.in

@@ -38,7 +38,7 @@ sys.path.append(os.path.join(LAMMPS_DOC_DIR, 'src', '_ext'))
 # -- General configuration ------------------------------------------------
 
 # If your documentation needs a minimal Sphinx version, state it here.
-#needs_sphinx = '1.0'
+needs_sphinx = '5.2.0'
 
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
@@ -53,10 +53,6 @@ extensions = [
     'tab_or_note',
     'breathe',
 ]
-# 2017-12-07: commented out, since this package is broken with Sphinx 16.x
-#             yet we can no longer use Sphinx 15.x, since that breaks with
-#             newer version of the multiprocessor module.
-#    'sphinxcontrib.images',
 
 images_config = {
   'default_image_width' : '25%',