Bug 26268: Remove items.paidfor from the database

Bug 26268: Remove items.paidfor from the database

In bug 19919 we removed all references to setting, unsettling and
referring to the paidfor field but we neglected to actually drop the
field from the database (I think I intended to do this, but was asking
for feedback on the approach before adding the actual db change.. then
completely forgot when it went through SO/QA quickly).

In bug 23463 we inadvertently re-introduced some of the setting code
during a rebase.

In bug 18501 we then moved that inadvertently re-introduced setter into
Koha::Item->store.

We should kill it off once and for all!

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>