remove required from sub-schema

lib/model-helper.js

@@ -81,6 +81,10 @@ var modelHelper = module.exports = {
         required.push(key);
       }
 
+      if (prop.hasOwnProperty('required')){
+        delete prop.required;
+      }
+
       // Change mismatched keys.
       prop = translateDataTypeKeys(prop);