Alter hold pickup lib from shelf avoids transit

Alter hold pickup lib from shelf avoids transit

When the pickup library for a hold is changed while the hold is on the
shelf, we no longer put the copy into transit to the new location.
Instead, we clear the shelf_expire_time (to prevent premature
expiration) and leave the hold and copy otherwise untouched.

This makes it possible for staff to identify items that are sitting on
the holds shelf that need to be put into transit to a new pickup
library.  The transit will be created when the item is checked in at the
originating library.

Signed-off-by: Bill Erickson <berick@esilibrary.com>