Remove unreferenced footnotes to fix Sphinx warnings

The PEPs and CPython PR are already linked inline throughout the text.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gpshead

peps/pep-9999.rst

@@ -319,16 +319,6 @@ Thanks to Nathaniel J. Smith for the original idea suggestion, and to
 dcolascione for initial review feedback on the implementation.
 
 
-References
-==========
-
-.. [1] `CPython PR #129337 <https://github.com/python/cpython/pull/129337>`_
-
-.. [2] :pep:`654` -- Exception Groups and except*
-
-.. [3] :pep:`678` -- Enriching Exceptions with Notes
-
-
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