test: core: Remove unneeded #include <platform_irq.h>

It's not used, and interferes when a platform doesn't have this file.

Change-Id: Icbffa7e912f297cbeaf4d1edfbd20fdf96efcacd
Signed-off-by: Øyvind Rønningstad <oyvind.ronningstad@nordicsemi.no>
1 file changed