net: remove HIPPI support and RoadRunner HIPPI driver

HIPPI has not been relevant for over two decades. It was rapidly
eclipsed by Fibre Channel, and even when it was new, it was
confined to very high-end hardware. The HIPPI code has only
received tree-wide changes and fixes by inspection in the entire
Git history. Remove HIPPI support and the rrunner HIPPI driver,
and move the former maintainer to the CREDITS file. Keep the
include/uapi/linux/if_hippi.h header because it is used by the TUN
code, and to avoid breaking userspace, however unlikely that may be.

Signed-off-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Link: https://patch.msgid.link/20260119022451.22344-1-enelsonmoore@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

CREDITS

@@ -3801,6 +3801,10 @@ S: Post Office Box 500
 S: Batavia, Illinois 60510
 S: USA
 
+N: Jes Sorensen
+E: jes@trained-monkey.org
+D: HIPPI support and Essential RoadRunner driver
+
 N: Leo Spiekman
 E: leo@netlabs.net
 W: http://www.netlabs.net/hp/leo/