ACPI S3: Remove unused acpi_is_wakeup_s4()

Change-Id: Id4728b637c784ee2bff7b175e13f4c10419b7f1b
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47692
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/arch/x86/acpi_s3.c

@@ -41,11 +41,6 @@ int acpi_is_wakeup_s3(void)
 	return (acpi_slp_type == ACPI_S3);
 }
 
-int acpi_is_wakeup_s4(void)
-{
-	acpi_handoff_wakeup();
-	return (acpi_slp_type == ACPI_S4);
-}
 #endif /* ENV_RAMSTAGE */
 
 #define WAKEUP_BASE 0x600