Virtualenv tries to copy it.
See https://github.com/pypa/virtualenv/issues/1352
Virtualenv ~16.6 warns:
No LICENSE.txt / LICENSE found in source
Technically, it is probably possible to install the package without
%license files, but that would simply resort to the previous noncritical
behavior.
This fix is not critical and hence it doesn't bump release, for easier
backporting to all our Python packages.
7fc9514b60