function tweakLhrForPsi(sampleLhr) {
  /** @type {LH.Result} */
  const clone = JSON.parse(JSON.stringify(sampleLhr));
  clone.categories = {
    'performance': clone.categories.performance,
  };
  return clone;
}
Drops the LHR to only one, solo category (performance).
@param {LH.Result} sampleLhr