Bug 19038: Remove the OPACShowBarcode syspref

Bug 19038: Remove the OPACShowBarcode syspref

This patch removes the OPACShowBarcode syspref in favour of the new
columns settings option introduced by bug 16759.

On the upgrade step, it picks the value for OPACShowBarcode and uses it
to populate the columns_settings table.

To test:
- Verify the upgrade process maintains the current behaviour

Regards

Sponsored-by: Dover

Followed test plan and works as expected. Functionality of patch from bug 16759
appears intact too.
Signed-off-by: Dilan Johnpullé <dilan@calyx.net.au>

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>