win: refactor get_windows_version()

win: refactor get_windows_version()

It's 2025, and almost all clients now run on Windows 10 or newer.
Instead of displaying:

  "Windows version 10.0 (Windows 10 or greater), amd64 executable"

we now show the exact build number, e.g.:

  "Windows version: 10.0.22631,amd64"

Remove "pre-Win7" checks in a few places.

Change-Id: I39d660ebeec76280e4d4357192b74bf2c0980615
Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20250505122712.5214-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg31566.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>