docs: retire the counted numbers that tests and the python-versions updater pin #1811

Describe the bug
Under the #1103 ruling (no counted numbers in the docs), several docs pages state counts that tests or tools pin, so their prose cannot change without the code:

• tests/project/test_conventions_doc_claims.py pins the process.rst changelog-entry and section counts, the registry-protocol.rst audit figures, and the helper and sentinel-reference counts.
• tests/corekit/test_sentinel_exports_unit.py pins the sentinel-convention.rst sentinel tally.
• tests/project/test_workflows_at_a_glance_1732.py pins the workflow count in workflows.rst.
• tests/project/test_python_matrix_tiers_1633.py, test_python_versions_1660.py and test_python_versions_update_1660.py pin, and the python-versions updater in util/ rewrites, the leg counts in workflows.rst and releasing.rst.

These figures drift, which is why the pins and the rewriter exist.

Expected behavior
The pinned prose becomes count-free in the same change that retires its pins. Each pin is either deleted or replaced by a check that still guards the underlying fact, for example that every workflow file has a row, without a number in the prose. The updater's count claims go too, while its version claims stay.

Additional context
From the #1103 counted-numbers inventory (frozen main d1f671738, results in the session's /tmp/counts-inventory/). The unpinned counts are prose and belong to #1103's round 3.