Link against KIOCore instead of KIOWidgets in kioslaves
Summary: The ioslaves don't need KIOWidgets, KIOCore is enough
Test Plan: builds
Reviewers: Baloo, apol, ngraham
Reviewed By: Baloo, apol, ngraham
Subscribers: kde-frameworks-devel
Tags: Frameworks, Baloo
Differential Revision: https://phabricator.kde.org/D22683