This is a vestige from [c5f3b28 "Fix Internet Archive book downloads"] that
left the old get_download_links() call (that takes no arguments) in one spot:

  1536588489.051963 ERROR root: SOURCE Internet Archive
  1536588489.052914 ERROR root: Searching URL http://bookserver.archive.org/catalog/alpha.xml headers {}
  Traceback (most recent call last):
    File "/home/lkundrak/src/get-books-activity/GetIABooksActivity.py", line 840, in __query_updated_cb
      self.catalogs_updated(query, midway)
    File "/home/lkundrak/src/get-books-activity/GetIABooksActivity.py", line 866, in catalogs_updated
      download_links = catalog_item.get_download_links()
  TypeError: get_download_links() takes exactly 4 arguments (1 given)