net: dsa: Remove redundant MDB dump support

Currently the MDB HW database is synced with the bridge's one, thus,
There is no need to support special dump functionality.

Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>