mlxsw: spectrum: Stop ignoring learning notifications from redirected traffic

As explained in the previous patch, with the ignore action prepended to
the redirect action, it is not longer possible for redirected traffic to
generate learning notifications.

Therefore, remove the workaround that was added in commit 577fa14d
("mlxsw: spectrum: Do not process learned records with a dummy FID") as
it is no longer needed.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>