Bug 18501: (follow-up) Remove duplicate test

Bug 18501: (follow-up) Remove duplicate test

The ModItem test found in t/db_dependent/Items.t was a duplciate (but
slightly less functional) for the test we introduced for the *_on
trigger functionality in t/db_dependent/Koha/Items.t::store

The failure was a missing C4::Context mock, but the logical fix is to
simply remove the duplicate test.

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