[OFW] Delete redundant strcasecmp function

components/drivers/ofw/base.c

@@ -333,8 +333,6 @@ static int ofw_prop_index_of_string(struct rt_ofw_prop *prop, const char *string
 
 static rt_int32_t ofw_strcasecmp(const char *cs, const char *ct)
 {
-    extern rt_int32_t strcasecmp(const char *cs, const char *ct);
-
     return rt_strcasecmp(cs, ct);
 }