llc2: Remove dead code for state machine

The initial state is UP and there is no way to enter the other states
as the required event type is never generated.  Delete all states,
event types, and other dead code.  The only thing left is handling
of the XID and TEST commands.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>