Return paths to GCS files in the given dataset directory.

def gcs_dataset_info_files(dataset_dir):
  """Return paths to GCS files in the given dataset directory."""
  prefix = posixpath.join(GCS_DATASET_INFO_DIR, dataset_dir, "")
  # Filter for this dataset
  filenames = [el for el in gcs_files(prefix_filter=prefix)
               if el.startswith(prefix) and len(el) > len(prefix)]
  return filenames