Simplify sphinx-gallery intersphinx config

According to its docs, there's no need for any additional entries in
`reference_url` if intersphinx is being used.

Author: QuLogic

doc/conf.py

@@ -190,8 +190,6 @@ def matplotlib_reduced_latex_scraper(block, block_vars, gallery_conf,
     'doc_module': ('matplotlib', 'mpl_toolkits'),
     'reference_url': {
         'matplotlib': None,
-        'numpy': 'https://numpy.org/doc/stable/',
-        'scipy': 'https://docs.scipy.org/doc/scipy/',
     },
     'backreferences_dir': Path('api') / Path('_as_gen'),
     'subsection_order': gallery_order.sectionorder,