mb/google/rex/var/screebo: remove SD_ABSENT

Remove SD_ABSENT since it's not being used, and CBI FW_CONFIG
in current build does not reflect this config neither.

BUG=b:291155207
TEST=emerge-rex coreboot

Change-Id: Icfa472ff5570ac728038ec67a762289407760812
Signed-off-by: YH Lin <yueherngl@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77596
Reviewed-by: Subrata Banik <subratabanik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/rex/variants/screebo/overridetree.cb

@@ -19,9 +19,8 @@ fw_config
 		option TOUCHSCREEN_ELAN		2
 	end
 	field DB_SD 11 12
-		option SD_ABSENT 0
-		option SD_GL9750 1
-		option SD_RTS5227S 2
+		option SD_GL9750		0
+		option SD_RTS5227S		1
 	end
 end