Bug 7534: Display pickup locations instead of all libraries in opac-reserve.pl

Bug 7534: Display pickup locations instead of all libraries in opac-reserve.pl

This patch sets opac-reserve.tt to use the list of pickup libraries instead
of every library in the system.

To test:
1. Go to cgi-bin/koha/admin/branches.pl
2. Configure one of your libraries to "Pickup location" => "No"
3. Go to OPAC and place a hold
4. See the provided Pickup location list
5. Observe the library that you configured is not present in the list

Signed-off-by: Koha Team AMU <axelle.clarisse@univ-amu.fr>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>