Bug 17946: Show number of subscriptions on tab in OPAC record details

Bug 17946: Show number of subscriptions on tab in OPAC record details

This patch removes some duplicate code.

To test:
1) Edit at least one subscription (or add a new one) to have a record
2) Find that record on the OPAC
3) Confirm that the Subscriptions tab reads the correct number of
subscriptions attached to the record

Sponsored-by: Catalyst IT
Signed-off-by: JMBroust <jean-manuel.broust@univ-lyon2.fr>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>