Update text of GPL to latest version from FSF

Update text of GPL to latest version from FSF

This mostly removes the postal address of the FSF.

This was triggered by rpmlint complaining about
that address being outdated.

Change-Id: Idfe5c615d1109a1038207c1c1b0e0de4da3279f5
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20250803143939.15335-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg32475.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 632573834ab8b4ddfc7d940347ecff05fbf3ff4b)