Remove explicit package dependency

package was previously an explicit dependency because it was pinned in pytest-dev#10578, however since then the pin has been removed, so the explicit dependency is no longer necessary.

doc/en/requirements.txt

@@ -5,10 +5,6 @@ sphinx-removed-in>=0.2.0
 sphinx>=7
 sphinxcontrib-trio
 sphinxcontrib-svg2pdfconverter
-# Pin packaging because it no longer handles 'latest' version, which
-# is the version that is assigned to the docs.
-# See https://github.com/pytest-dev/pytest/pull/10578#issuecomment-1348249045.
-packaging
 furo
 sphinxcontrib-towncrier
 sphinx-issues