Remove Kleo dependency

Akonadi-contacts currently depends on Libkleo for two properties in ContactGrantleeWrapper, signaturePreference and cryptoPreference. However, these are not used in any Akonadi-enabled applications and the only reference I could find to either of them was in a README file for KAddressBook here: https://invent.kde.org/pim/kaddressbook/-/blob/master/src/printing/grantlee/README.themes#L104

This MR therefore drops these preferences, allowing for the removal of the Libkleo dependency entirely