Fix #131: Move unix-uname to contrib/unix
unix:unix-uname
is no longer used in any core cmucl functions, so it
can be removed from src/code/unix.lisp. We move it to
src/contrib/unix/unix-glibc2.lisp (for x86) and
src/contrib/unix/unix.lisp (for all other archs).
Remove unix-uname
from the unix package too.
cmucl-unix.pot is updated because the docstring is gone now.