net: dsa: microchip: Remove unused ksz8_all_queues_split()

ksz8_all_queues_split() isn't used anywhere.

Remove it.

Signed-off-by: Bastien Curutchet (Schneider Electric) <bastien.curutchet@bootlin.com>
Link: https://patch.msgid.link/20260505-clean-ksz-driver-v1-1-05d70fa42461@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>