Bug 30481: Drop unique constraint deleteditemsstocknumberidx

Bug 30481: Drop unique constraint deleteditemsstocknumberidx

Resolves a sync issue between database and schema caused by
differences between structure and upgrades. Note: newer
databases do not contain this index any longer.

Test plan:
Run dbrev.
Check SHOW CREATE TABLE deleteditems.
Verify that unique index has been dropped, regular index added.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>