PEP 634: Fix duplicate labels

[hugovk]

Fix these warnings (like we did in #2718):

pep-0634.rst:140: WARNING: duplicate label guards, other instance in pep-0622.rst
pep-0634.rst:175: WARNING: duplicate label patterns, other instance in pep-0622.rst
pep-0634.rst:231: WARNING: duplicate label literal_pattern, other instance in pep-0622.rst
pep-0634.rst:267: WARNING: duplicate label capture_pattern, other instance in pep-0622.rst
pep-0634.rst:290: WARNING: duplicate label wildcard_pattern, other instance in pep-0622.rst
pep-0634.rst:337: WARNING: duplicate label sequence_pattern, other instance in pep-0622.rst
pep-0634.rst:417: WARNING: duplicate label mapping_pattern, other instance in pep-0622.rst
pep-0634.rst:472: WARNING: duplicate label class_pattern, other instance in pep-0622.rst
pep-0634.rst:598: WARNING: duplicate label appendix a, other instance in pep-0622.rst

Sphinx treats labels as "global" in the whole docs scope, not at the level of individual documents. So let's use a unambiguous label prefixed with the PEP number, similar to PEP 639 / https://raw.githubusercontent.com/python/peps/main/pep-0639.rst

We still get similar anchors like #guards:

• https://peps.python.org/pep-0634/#guards
• https://pep-previews--2735.org.readthedocs.build/pep-0634/#guards

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Also remove redundant emacs metadata.

Preview

https://pep-previews--2735.org.readthedocs.build/pep-0634/

[CAM-Gerlach]

LGTM, thanks @hugovk