Stop explicitly listing wheel as a build dependency

setuptools' get_requires_for_build_wheel() hook already injects this dependency
when building wheels is requested.

See also 64d8938.

news/12728.feature.rst

@@ -0,0 +1,5 @@
+``wheel`` is no longer explicitly listed as a build depepndency of ``pip``.
+``setuptools`` already injects this dependency in the ``get_requires_for_build_wheel()`` hook.
+This makes no difference for users of ``pip``.
+This makes no difference when building wheels of ``pip``.
+This avoids an unnecessary dependency on ``wheel`` wehn bulding the source distribution of ``pip``.

pyproject.toml

@@ -41,7 +41,7 @@ Changelog = "https://pip.pypa.io/en/stable/news/"
 
 [build-system]
 # The lower bound is for <https:/pypa/setuptools/issues/3865>.
-requires = ["setuptools>=67.6.1", "wheel"]
+requires = ["setuptools>=67.6.1"]
 build-backend = "setuptools.build_meta"
 
 [tool.setuptools]