[Cuttlefish] Replace deprectated method KDeclarative::setupBindings()
Summary:
Replace method call like described in the documentation. Also we don't need to
cast &engine because a QQmlApplicationEngine is a QQmlEngine.
Test Plan: compiles
Reviewers: Plasma, apol
Reviewed By: apol
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D25842