Fix Sphinx tutorial seealso links (#11806)

This had redundant links and a link without description


![image](https://github.com/user-attachments/assets/899a3a20-0369-49a4-8bac-4a997ecb7293)


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:books: Documentation previews :books:

- User's documentation (`docs`):
https://docs--11806.org.readthedocs.build/en/11806/

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- Developer's documentation (`dev`):
https://dev--11806.org.readthedocs.build/en/11806/

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docs/user/intro/sphinx.rst

@@ -133,9 +133,7 @@ You can now continue writing your docs in ``.md`` files and it will work with Sp
 .. seealso::
 
    `Getting started with MyST in Sphinx <https://myst-parser.readthedocs.io/en/latest/sphinx/intro.html>`_
-
-   :doc:`/guides/migrate-rest-myst`
-     Learn how to use references between different Sphinx projects, for instance between subprojects
+     Learn how to use MyST to write Markdown documentation in your Sphinx project.
 
    :doc:`/guides/migrate-rest-myst`
      Start writing Markdown in your existing reStructuredText project, or migrate it completely.