Remove dead link to pkg_resources

[woodruffw]

pkg_resources is no longer provided by setuptools, so this link is dead (and breaks the build). I've removed the link but kept the term itself, along with a mention of the removal.

Ref: https://discuss.python.org/t/pkg-resources-removal-how-to-go-from-there/106079

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📚 Documentation preview 📚: https://python-packaging-user-guide--2002.org.readthedocs.build/en/2002/

[woodruffw]

CC @pypa/packaging-user-guide-editors

[edgarrmondragon]

It's linked to in other places unfortunately:

packaging.python.org/source/guides/multi-version-installs.rst

Lines 41 to 43 in 11477a6

	Refer to the `pkg_resources documentation
	<https://setuptools.readthedocs.io/en/latest/pkg_resources.html#workingset-objects>`__
	for more details.

packaging.python.org/source/guides/packaging-namespace-packages.rst

Lines 288 to 289 in 11477a6

	.. _pkg_resources.declare_namespace:
	https://setuptools.readthedocs.io/en/latest/pkg_resources.html#namespace-package-support

[woodruffw]

It's linked to in other places unfortunately:

Grumble, thanks 🙂