Revert "gnutls: Update to latest old-stable branch release"

This reverts commit 4d7a5e003f6da46625f8492da9c21af9ba01c162.
old-stable branch presents problems within Evolve OS. Given we don't ship
this package yet, there isn't a security risk. In the near future we'll
update to 3.2 or later, and update libnettle to accomodate.