Remove more of distutils.

Not sure what this does but the end wheel/sdist are quasi identical.
So let's remove it.

MANIFEST.in

@@ -15,8 +15,6 b' exclude tools'
 exclude CONTRIBUTING.md
 exclude .editorconfig
 
-graft setupext
-
 graft scripts
 
 # Load main dir but exclude things we don't want in the distro

setupbase.py

@@ -24,7 +24,6 b' from setuptools.command.build_py import build_py'
 from setuptools.command.install import install
 from setuptools.command.install_scripts import install_scripts
 
-from setupext import install_data_ext
 
 #-------------------------------------------------------------------------------
 # Useful globals and utility functions
@@ -65,7 +64,6 b' setup_args = dict('
       author           = author,
       author_email     = author_email,
       license          = license,
-      cmdclass         = {'install_data': install_data_ext},
       )