Update instructions for Jupyter notebook galleries (#11545)

* Update instructions for Jupyter notebook galleries

* Remove sentence about Sphinx-Gallery

* Remove another mention of Sphinx-Gallery

Author: mgeier

docs/user/guides/jupyter.rst

@@ -237,21 +237,8 @@ Creating galleries of examples using notebooks
 
 `nbsphinx`_ has support for :doc:`creating thumbnail galleries from a list of Jupyter
 notebooks <nbsphinx:subdir/gallery>`.
-This functionality relies on `Sphinx-Gallery <https://sphinx-gallery.github.io/>`_
-and extends it to work with Jupyter notebooks rather than Python scripts.
 
-To use it, you will need to install both nbsphinx and Sphinx-Gallery,
-and modify your ``conf.py`` as follows:
-
-.. code-block:: python
-   :caption: conf.py
-
-   extensions = [
-       "nbsphinx",
-       "sphinx_gallery.load_style",
-   ]
-
-After doing that, there are two ways to create the gallery:
+There are two ways to create the gallery:
 
 - From a reStructuredText source file, using the ``.. nbgallery::`` directive,
   :ref:`as showcased in the
@@ -266,9 +253,7 @@ After doing that, there are two ways to create the gallery:
 
    Panel to modify cell metadata in JupyterLab
 
-For example, this reST markup would create a thumbnail gallery
-with generic images as thumbnails,
-thanks to the Sphinx-Gallery default style:
+For example, this markup would create a thumbnail gallery:
 
 .. tabs::