switchdev: mrp: Remove SWITCHDEV_ATTR_ID_MRP_PORT_STAT

Now that MRP started to use also SWITCHDEV_ATTR_ID_PORT_STP_STATE to
notify HW, then SWITCHDEV_ATTR_ID_MRP_PORT_STAT is not used anywhere
else, therefore we can remove it.

Fixes: c284b545

 ("switchdev: mrp: Extend switchdev API to offload MRP")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>