setup: Remove requirement "wheel".

"wheel" is not required for building, but only for creating the
distribution package in ".whl" format. The package builds fine into a
bdist archive without "wheel".

pyproject.toml

@@ -5,7 +5,6 @@
 requires =[
         "setuptools >=39.2.0",
         "setuptools_scm >= 4.1.2",
-        "wheel",
         ]
 
 build-backend = "setuptools.build_meta"

setup.cfg

@@ -34,7 +34,6 @@ install_requires =
 setup_requires =
     setuptools >=39.2.0
     setuptools_scm >= 4.1.2
-    wheel
 [options.extras_require]
 # To install these dependencies, run pip install .[test]
 test =