Bug 21548: ILLLIBS patron category / partner_code seems extraneous

Bug 21548: ILLLIBS patron category / partner_code seems extraneous

This patch updates the default partner category used by the partner_code config to be in line with sample data in sample_patrons.yml

Preparation:
Apply patch
Enable ILLModule sys pref
Install an ILL backend (e.g. FreeForm)
Add this change to your koha-conf.xml
Flush, restart.
Search for patron of category inter-library loan and assign a primary e-mail address to it

Test plan:
Create an ILL request and click 'place request with partners'
Verify that the 'select partner libraries' has the correct patron of IL category

Run tests and ensure they pass:
prove t/db_dependent/Illrequest/Config.t
prove t/Koha/Config.t

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>