net: bridge: Remove FDB deletion through switchdev object

At this point no driver supports FDB add/del through switchdev object
but rather via notification chain, thus, it is removed.

Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Ivan Vecera <ivecera@redhat.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>