code: public static boolean deleteProperty(Scriptable obj, int index)
      {
          Scriptable base = getBase(obj, index);
          if (base == null)
              return true;
          base.delete(index);
          return !base.has(index, obj);
      }
docs: Removes the property from an object or its prototype chain.
  <p>
  Searches for a property with <code>index</code> in obj or
  its prototype chain. If it is found, the object's delete
  method is called.
  @param obj a JavaScript object
  @param index a property index
  @return true if the property doesn't exist or was successfully removed
  @since 1.5R2