Bug 29617: exclude categorycode from BorrowerUnwantedField

Bug 29617: exclude categorycode from BorrowerUnwantedField

To test:
1. Go to BorrowerUnwantedField and select categorycode as unwanted
2. Try adding a new patron, you will see an error message in the staff client "Something went wrong when creating the patron. Check the logs." You will be unable to make a new patron.
3. Apply patch
4. Go to BorrowerUnwantedField, you are unable to exlcude it. Patrons need categorycodes

Signed-off-by: Emmanuel Bétemps <e.betemps@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>