Bug#919835: mgba; AppStream metadata isn't being used because of its license

[Jeremy Bicha]

Source: mgba
Version: 0.6.3+dfsg1-2
X-Debbugs-CC: sergio_br2 at yahoo.com.br

The AppStream metadata that was added to the Debian package isn't
being used because its metadata_license isn't on the short list of
approved licenses.

I encourage you to consider relicensing your metadata as CC0-1.0. From
what I can tell, CC0-1.0 is by far the most popular license for
AppStream metadata.

The AppStream metadata for libretro-mgba isn't very useful for
gnome-games-app without the .libretro file. It would be easier for me
to help with some of these issues if these projects used
https://salsa.debian.org . Please let me know if you would like my
help.

References
----------------
https://appstream.debian.org/sid/main/issues/libretro-mgba.html
https://github.com/ximion/appstream/blob/master/src/as-spdx.c#L449-L478
https://bugs.debian.org/911327
https://bugs.debian.org/872484

Thanks,
Jeremy Bicha