code: public void delete(String key) throws EtcdClientException {
          Preconditions.checkNotNull(key);
  
          URI uri = buildUriWithKeyAndParams(key, null);
          HttpDelete delete = new HttpDelete(uri);
  
          syncExecute(delete, new int[]{200, 404});
      }
docs: Delete a key
  @param key the key
  // @return operation result