Remove deprecated license_file from setup.cfg (#182)

Starting with wheel 0.32.0 (2018-09-29), the "license_file" option is
deprecated.

https://wheel.readthedocs.io/en/stable/news.html

The wheel will continue to include LICENSE, it is now included
automatically:

https://wheel.readthedocs.io/en/stable/user_guide.html#including-license-files-in-the-generated-wheel-file

setup.cfg

@@ -4,9 +4,6 @@ test=pytest
 [bdist_wheel]
 universal = 1
 
-[metadata]
-license_file = LICENSE
-
 [tool:pytest]
 addopts = -v
 python_files = test.py