Bug#915919: mixxx: Uses vendor-specific patch series file (ubuntu.series)

[Jeremy Bicha <jbicha@debian.org>]

It looks like the only patch that is intentionally different between
Debian and Ubuntu is that 0002-desktop_file.patch is not applied on
Ubuntu.

I think that patch could be either removed or applied on Ubuntu too.

If you decide you do want to continue to have different behavior on
Ubuntu, you could use something like
https://salsa.debian.org/desktop-themes-team/numix-gtk-theme/commit/488a7f83
instead.

Thanks,
Jeremy Bicha