Bug 26999: (follow-up) Simplify code

Bug 26999: (follow-up) Simplify code

Doing
$ git grep pickup_locations_code

shows there's some calculated data that is not actually used anywhere.
We can get rid of it.

This patch also reuses $item_object (which is in the same loop scope) to
avoid an extra DB call.

To test:
1. Run:
   $ git grep pickup_locations_code
=> FAIL: It is only used/set as a comma separated string, inside
request.pl
2. Apply this patch
3. Repeat 1
=> SUCCESS: The unused stuff is not there anymore
4. Open the page for placing some holds
=> SUCCESS: It doesn't explode
5. Sign off :-D

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>