Bug 23150: Do not consider gdpr_proc_consent a mandatory field

Bug 23150: Do not consider gdpr_proc_consent a mandatory field

It introduced a regression in the patron's self modification feature.
Patron's details are no longer modificable, the screen displays
"You have not filled out all required fields. Please fill in all missing
fields and resubmit."

Test plan:
- Set GDPR_Policy to either Enforced or Permissive
- Set PatronSelfRegistrationBorrowerMandatoryField to empty
- Set OPACPatronDetails to Allow
- Log into the OPAC
- Accept the GDPR screen
- Go to opac-memberentry.pl, change something, submit modification
request

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>