AMD Olive Hill: Enable WARNINGS_ARE_ERRORS (remove override)

Change-Id: Idf26eb3fb541355bd9553c1897f647738c347eb5
Signed-off-by: Bruce Griffith <bruce.griffith@se-eng.com>
Reviewed-by: Dave Frodin <dave.frodin@se-eng.com>
Reviewed-on: http://review.coreboot.org/3819
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martin.roth@se-eng.com>

src/mainboard/amd/olivehill/Kconfig

@@ -97,8 +97,4 @@ config HUDSON_LEGACY_FREE
 	bool
 	default y
 
-config WARNINGS_ARE_ERRORS
-	bool
-	default n
-
 endif # BOARD_AMD_OLIVEHILL