Bug 22646: Fix use of PrivacyPolicyURL

Bug 22646: Fix use of PrivacyPolicyURL

To test:

PatronSelfRegistration = Allow
PatronSelfRegistrationDefaultCategory = PT (or some other real category)
GDPR_Policy = Enforced
PrivacyPolicyURL = Some URL

- Go to <opac>/cgi-bin/koha/opac-memberentry.pl and verify that the text "privacy
  policy" displays a link to the current page, not the URL in PrivacyPolicyURL
- Go to Administration > System preferences > Patrons > Privacy
- Verify that the descriptions of GDPR_Policy and PrivacyPolicyURL does not
  mention that PrivacyPolicyURL needs to be set if GDPR_Policy is set.
- Apply the patch
- Verify that opac-memberentry.pl now links to the URL in PrivacyPolicyURL
- Verify that the syspref descriptions mention the relationship between them

Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Bin Wen <bin.wen@inlibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>