Revert "mainboard/lenovo/x230: Add ThinkPad x230s as a variant"

This reverts commit 6b95507ec5, in order
to recommit and review it again.

Change-Id: Id4ddf99200f77016a48d02a8421d080cea492aae
Signed-off-by: Bill XIE <persmule@hardenedlinux.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41504
Reviewed-by: Alexander Couzens <lynxis@fe80.eu>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/mainboard/lenovo/Ivy_Bridge_series.md

@@ -1,6 +1,6 @@
 # Lenovo Ivy Bridge series
 
-This information is valid for all supported models, except T430s, [T431s](t431s.md) and [X230s](x230s.md).
+This information is valid for all supported models, except T430s and T431s.
 
 ## Flashing coreboot
 ```eval_rst