Bug 18605: Remove TRUNCATE from C4/HoldsQueue.pm

Bug 18605: Remove TRUNCATE from C4/HoldsQueue.pm

Replaces TRUNCATE by DELETE, since truncate implicitly commits. We don't
need to do that here. (Would complicate testing it too.)
Fixes typo disablig.
Add a simple test to HoldsQueue.t.

Test plan:
Run t/db_dependent/HoldsQueue.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>