include/acpi/acpi.h: Drop non-existing update_ssdtx()

Change-Id: I2fd8470ed2b8e8f00de4ba64258aac1db52744c1
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62120
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/include/acpi/acpi.h

@@ -1233,7 +1233,6 @@ void acpi_fill_gnvs(void);
 void acpi_fill_cnvs(void);
 
 void update_ssdt(void *ssdt);
-void update_ssdtx(void *ssdtx, int i);
 
 unsigned long acpi_fill_lpit(unsigned long current);