Remove deprecated `license_file` option
Remove deprecated `license_file` option

Starting with wheel 0.32.0 (2018-09-29), the `license_file` option is
deprecated in favor of `license_files`.

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

See https://github.com/FactoryBoy/factory_boy/pull/696 for inspiration and more discussion.
drewja/flask,pallets/flask,fkazimierczak/flask,drewja/flask,mitsuhiko/flask,drewja/flask,fkazimierczak/flask,pallets/flask,mitsuhiko/flask,pallets/flask,fkazimierczak/flask