cloud9-image: remove gateone

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
bone101: remove references to GateOne SSH client

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
bone101: fix dead links

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>