Bug 27261: exlude branchcode from PatronSelfRegistrationBorrowerUnwantedField

Bug 27261: exlude branchcode from PatronSelfRegistrationBorrowerUnwantedField

To test:
1 - Alter PatronSelfRegistrationBorrowerUnwantedFieldand select branchcode
2 - Attempt to self register via the OPAC
3 - Kabloom, internal server error
4 - Apply patche
5 - Alter the preference again
6 - Note that branchcode is unchecked and disabled
7 - Save the pref
8 - Attempt to self register again
9 - It succeeds

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>