mlxsw: spectrum_router: Remove unnecessary checks

Now that the networking stack takes care of only notifying the routes of
interest, we do not need to maintain a list of identical routes.

Remove the check that tests if the route is the first route in the FIB
node.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>