function getModelPathFromKey(key) {
    const items = key.split(PATH_SEPARATOR);
    if (items.length < 3) throw new Error(`Invalid key format: ${key}`);
    return items.slice(1, items.length - 1).join(PATH_SEPARATOR);
}
Get model path from a local-storage key.

E.g., 'tensorflowjs_models/my/model/1/info' --> 'my/model/1'

@param key