Bug 26995: Drop column relationship from borrowers, deletedborrowers and borrower_mod...

Bug 26995: Drop column relationship from borrowers, deletedborrowers and borrower_modifications tables

Bug 14570 added a borrower_relationships table but it didn't remove the relationship column from the following tables:
- deletedborrowers
- borrowers
- borrower_modifications

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