comms/nec2c: Fix bogus licence

I've only just noticed the author put this into public domain
as the original was public domain. He only stressed the wish
to keep it FOSS.

 7. License:
  nec2c is Public Domain, same as the original FORTRAN source.
  Please keep any software you write incorporating nec2c in Public
  Domain or at least use an open license like GPL or BSD.

I believe this was his intent but having a GPL COPYING file
certainly confuses things.