- Do not require python3-magic: lutris has its own, intree version
of magic.py.

Please help test this, my knowledge of lutris is too limited.
What I can see though: lutris brings it's own magic.py and does not
seem to rely on an external python-magic.

If it would, we have to be careful to provide it with the right variant though, as there are:
* python-magic (from libmagic)
* python-python-magic (package provided on pypi)

If, any, then the code seems more to be willing to work with the pypi version, which implies
that the current dep on python3-magic is not used at all (as I'd expect)