apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/txtresolver/PropertyResolver.java/PropertyResolver/deleteNormalKVItem
class PropertyResolver:  private void deleteNormalKVItem(Map<String, ItemDTO> baseKeyMapItem, ItemChangeSets changeSets) {
    //surplus item is to be deleted
    for (Map.Entry<String, ItemDTO> entry : baseKeyMapItem.entrySet()) {
      changeSets.addDeleteItem(entry.getValue());
    }
  }