Bug 19857: Use BorrowerUnwantedField system preference for SMS provider selection

Bug 19857: Use BorrowerUnwantedField system preference for SMS provider selection

Optionally hide SMS provider field in patron modification screen with
BorrowerUnwantedField system preference.

To test:
1. Apply patch
2. Append BorrowerUnwantedField with sms_provider_id and save changes
3. Go to patron modification screen in staff client
4. Observe the SMS provider selection is now hidden

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>