security: replace FSF address with web source in license notices

A few years ago the FSF moved and "59 Temple Place" is wrong. Having this
still in our source files feels old and unmaintained.

Let's take the license statement serious and not confuse users.

As https://www.gnu.org/licenses/gpl-howto.html suggests, we replace the
postal address with "<http://www.gnu.org/licenses/

>" in the security
directory.

Signed-off-by: Martin Kepplinger <martink@posteo.de>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>