code: function removeMirrorID({mirror, ...args}) {
    return withPromise((resolve) => {
      mirror.removeAttribute('id');
      delete mirror.id;
      resolve({mirror, ...args});
    });
  }
docs: Removes source ID from cloned mirror element
  @param {Object} state
  @param {HTMLElement} state.mirror
  @return {Promise}
  @private