zaius: Remove psi_set_external_irq_policy from platform init

This function is specific to how Skiboot's P8 PSIHB driver. For P9 the
PSIHB driver has been reworked completely and this doesn't do anything.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Acked-By: Michael Neuling <mikey@neuling.org>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

platforms/astbmc/zaius.c

@@ -31,7 +31,6 @@ static bool zaius_probe(void)
 
 	/* Lot of common early inits here */
 	astbmc_early_init();
-	psi_set_external_irq_policy(EXTERNAL_IRQ_POLICY_LINUX);
 
 	/* Setup UART for direct use by Linux */
 	uart_set_console_policy(UART_CONSOLE_OS);