Bug 7534: Display pickup locations instead of all libraries in request.pl

Bug 7534: Display pickup locations instead of all libraries in request.pl

This patch sets request.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 place a hold in intranet
4. See the provided "Pickup at" list
5. Observe the library that you configured is not present in the list
6. Place the hold
7. See list of existing holds on that biblio
8. See "Pickup library" column and observe your configured library is
   not included in the list

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