Remove extending/windows from toctree

Author: AA-Turner

Doc/extending/index.rst

@@ -92,7 +92,6 @@ C extensions.
 * :ref:`defining-new-types`
 * :ref:`new-types-topics`
 * :ref:`building`
-* :ref:`building-on-windows`
 
 Embedding the CPython runtime in a larger application
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