src: Remove unused 'include <arch/smp/mpspec.h>'

Change-Id: If8048586e3693a8e6f63d9dc2800b073bab78628
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41669
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: David Guckian
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/slippy/acpi_tables.c

@@ -2,7 +2,6 @@
 
 #include <types.h>
 #include <acpi/acpi.h>
-#include <arch/smp/mpspec.h>
 #include <device/device.h>
 #include <vendorcode/google/chromeos/gnvs.h>
 #include <ec/google/chromeec/ec.h>