mlxsw: spectrum_router: Remove batch neighbour deletion causing FW bug

This reverts commit 63dd00fa.

RAUHT DELETE_ALL seems to trigger a bug in FW. That manifests by later
calls to RAUHT ADD of an IPv6 neighbor to fail with "bad parameter"
error code.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Fixes: 63dd00fa ("mlxsw: spectrum_router: Add batch neighbour deletion")
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>