mb/libretrend/Kconfig: Remove duplicated string

Change-Id: Iab19538e1f5a74b714cb2a34855d9717315b9018
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49884
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by:  Felix Singer <felixsinger@posteo.net>

src/mainboard/libretrend/Kconfig

@@ -10,7 +10,6 @@ endchoice
 source "src/mainboard/libretrend/*/Kconfig"
 
 config MAINBOARD_VENDOR
-	string "Mainboard Vendor"
 	default "Libretrend"
 
 endif # VENDOR_LIBRETREND