mb/opencellular/elgon/Kconfig: Drop unused 'MAINBOARD_FIT_DTS'

Change-Id: Ie084f93998dc16450bb3db99d7240905bed3d50e
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45067
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/opencellular/elgon/Kconfig

@@ -72,8 +72,4 @@ config MAINBOARD_PART_NUMBER
 	string
 	default "Elgon"
 
-config MAINBOARD_FIT_DTS
-	string
-	default "gbcv2.dts"
-
 endif