The only API user currently seems to be the examples. fprintd has its
own storage and that will be a good idea in general.
So deprecate the API, we'll need to find a different solution for the
examples eventually.
The function was committed by accident as part of commit d18e1053
(lib: Add a way to name timeouts). It is not used anywhere and
fpi_timeout_cancel_all_for_dev exists, is exported and used and serves
the same purpose.