build: no need for setup.cfg

It's a little unfortunate that we're moving a seting INTO setup.py, but
at least it lets us get rid of one metadata file.

Author: nedbat

setup.cfg

@@ -118,6 +118,7 @@
     long_description_content_type='text/x-rst',
     keywords='code coverage testing',
     license='Apache-2.0',
+    license_files=["LICENSE.txt"],
     classifiers=classifier_list,
     url="https://github.com/nedbat/coveragepy",
     project_urls={