Clean up unused arch/early_variables.h header

Change-Id: Ib863e23863ba6d7504b6c4d32de2f1fea4e57fec
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32996
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/mainboard/packardbell/ms2290/romstage.c

@@ -31,7 +31,6 @@
 #include <timestamp.h>
 #include <arch/acpi.h>
 
-#include "arch/early_variables.h"
 #include <southbridge/intel/ibexpeak/pch.h>
 #include <northbridge/intel/nehalem/nehalem.h>