remove redundant wheel dep from pyproject.toml

Remove the redundant `wheel` dependency, as it is automatically added
by the setuptools build-backend.  Listing it in `pyproject.toml`
was a historical documentation mistake that was fixed recently (see
pypa/setuptools@f7d30a9).

pyproject.toml

@@ -2,6 +2,5 @@
 # Further build requirements come from setup.py via the PEP 517 interface
 requires = [
     "setuptools>=42",
-    "wheel",
 ]
 build-backend = "setuptools.build_meta"