[kldap] Fix compilation without LDAP

Summary: Update the method signatures when not `LDAP_FOUND`

Test Plan: It compiles when `LDAP_FOUND` is not defined

Reviewers: #kde_pim, vkrause, dvratil

Reviewed By: #kde_pim, vkrause

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D26337