net: Remove bouncing hippi list

linux-hippi is bouncing with:

 <linux-hippi@sunsite.dk>:
 Sorry, no mailbox here by that name. (#5.1.1)

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>