Remove redundant wheel dep from pyproject.toml (#765)

The `wheel` dependency is added automatically by setuptools build
backend (since day one) and therefore should not be specified
explicitly.  Listing it in documentation was a historical mistake
and has been corrected since.  See:
pypa/setuptools@f7d30a9

pyproject.toml

@@ -1,5 +1,5 @@
 [build-system]
-requires = ["setuptools", "wheel"]
+requires = ["setuptools"]
 build-backend = "setuptools.build_meta"