mlxsw: spectrum_span: Remove old SPAN API

Remove the old SPAN API now that matchall-based and flower-based
mirroring were converted to use the new API.

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