mb/51nb/Kconfig: Remove duplicated string

Change-Id: Ib184dbfef05608bbf18d49fee5cbc9dd12ed6751
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49883
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by:  Felix Singer <felixsinger@posteo.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/51nb/Kconfig b/src/mainboard/51nb/Kconfig
index 5124fdb..d0efbc6 100644
--- a/src/mainboard/51nb/Kconfig
+++ b/src/mainboard/51nb/Kconfig
@@ -12,7 +12,6 @@
 source "src/mainboard/51nb/*/Kconfig"
 
 config MAINBOARD_VENDOR
-	string "Mainboard Vendor"
 	default "51NB"
 
 endif # VENDOR_51NB