Delete unnecessary 'in any medium' from copyright license grant.

This is ancient GPL phrasing. While harmless, I see no harm in
deleting it. The idea (the only objection I can anticipate) that the
deletion opens up some possible argument that some particular
*unspecified* 'medium' through which the copyright licensee exercises
the license grant is closed off through failure to say "in any medium"
is self-evidently preposterous.