net: x25: remove dead links from Kconfig

Remove the "You can read more about X.25 at" links provided in
Kconfig as they have not pointed at any relevant pages for quite
a while.

An old copy of https://www.sangoma.com/tutorials/x25/ can be
retrieved via https://archive.org/web/ but nothing useful seems
to have been preserved for http://docwiki.cisco.com/wiki/X.25

For the sake of necromancy and those who really did want to
read more about X.25, a previous incarnation of Kconfig included
a link to:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios11/cbook/cx25.htm

Which can still be read at:
https://web.archive.org/web/20071013101232/http://cisco.com/en/US/docs/ios/11_0/router/configuration/guide/cx25.html



Signed-off-by: Justin Swartz <justin.swartz@risingedge.co.za>
Acked-by: Martin Schiller <ms@dev.tdt.de>
Link: https://lore.kernel.org/r/20240306112659.25375-1-justin.swartz@risingedge.co.za


Signed-off-by: Jakub Kicinski <kuba@kernel.org>