Remove redundant wheel dep from pyproject.toml (#496)

Remove the redundant `wheel` dependency, as it is added by the backend
automatically.  Listing it explicitly in the documentation was
a historical mistake and has been fixed since, see:
pypa/setuptools@f7d30a9

pyproject.toml

@@ -1,3 +1,3 @@
 [build-system]
-requires = ["setuptools >= 46.4.0", "wheel"]
+requires = ["setuptools >= 46.4.0"]
 build-backend = "setuptools.build_meta"