Summary:
Resolves Bug 401255

Bonus: Disable some very noisy debugging from the SMS app

Test Plan:
 - Build KDE Connect with or without Kirigami
   - Verify successful build with no complaints about Kirigami
 - Build KDE Connect's Messenger:
   - Without Kirigami: Verify that CMake warns that Kirigami is not found
   - With Kirigami: Verify that app launches successfully

Reviewers: #kde_connect, nicolasfella

Reviewed By: #kde_connect, nicolasfella

Subscribers: apol, kdeconnect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D17572