Bug 28842: A summary to the /items/:item_id/pickup_locations route

Bug 28842: A summary to the /items/:item_id/pickup_locations route

This patch simply adds a summary to the route. This will be picked by
the API docs.

It also removes the 'pickup_locations' tag, as we did in bug 28461.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>