Bug 25946: borrowerRelationship can be empty

Bug 25946: borrowerRelationship can be empty

Do not split the config using comma.

From syspref description of borrowerRelationship preference:

> Guarantors can be the following of those they guarantee:
> (input multiple choices separated by |). Leave empty to deactivate.

As it doesn't mention comma at all, I removed ',' from split.
Of course if comma is actually a viable way to split separate choices,
I can obsolete this patch and append to the syspref description that it
also can be separated by comma.

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