utils/xz: fix license

utils/xz: fix license

Remove GPL-2.0+ and GPL-3.0+ from PKG_LICENSE as GNU GPLv2+ and GPLv3+
are only used for the build system as stated in [1]:

 The build system contains public domain files, and files that
 are under GNU GPLv2+ or GNU GPLv3+. None of these files end up
 in the binaries being built.

Moreover, add 0BSD which is used since version 5.6.0 [2]

[1]: https://github.com/tukaani-project/xz/commit/02ddf09bc3079b3e17297729b9e43f14d407b8fc
[2]: https://github.com/tukaani-project/xz/commit/689e0228baeb95232430e90d628379db89583d71

Fixes: b9e87eeb7deb8b3890415b835c9c69764893c023 (xz: import from old packages feed)
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>