python-enum: fix license information

python-enum: fix license information

The bump of python-enum to version 0.4.6 in commit
636df89872c7b6a6bed2c679cf65da41309ac652 forgot to update the license
information. Even though the PKG-INFO file still pretends it's GPLv2
or Python license, the only license file available is LICENSE.GPL-3
(which indicates a GPLv3 license), and the comment header in the
source code is pretty clear:

    This is free software: you may copy, modify, and/or distribute
    this work under the terms of the GNU General Public License as
    published by the Free Software Foundation; version 3 of that
    license or any later version.  No warranty expressed or
    implied. See the file ‘LICENSE.GPL-3’ for details.

Fixes:

   http://autobuild.buildroot.net/results/7fec1c7cde710f523263e74b1849f1f4488b7d26/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>