Bug 29523: Remove the FIXME

Bug 29523: Remove the FIXME

This patch works through the unit tests and existing code to allow
removal of the FIXME I introduced earlier in the patchset.

We now require the `user` parameter be passed to `is_accessible` which
in turn makes `user` a required parameter for `to_api` in the
`Koha::Patron` case.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>