remove unnecessary convert from Object to ResultMap

[mawen12]

I have found the method checkGloballyForDiscriminatedNestedResultMaps in class Configuration contains unnecessary convert code.

protected final Map<String, ResultMap> resultMaps = new StrictMap<>("Result Maps collection");

...

protected void checkGloballyForDiscriminatedNestedResultMaps(ResultMap rm) {
  if (rm.hasNestedResultMaps()) {
    ...
    for (Object resultMapObject : resultMaps.values()) {
     // here is unnecessary code
      if (resultMapObject instanceof ResultMap) {
        ResultMap entryResultMap = (ResultMap) resultMapObject;
        ...
      }
    }
  }
}

Because variable resultMaps is Map<String, ResultMap>, so it's value type is ResultMap, no need convert from Object.