Remove WaylandDialogFilter

Summary:
now that KWayland is a framework, it's used directly from
Dialog, no need to inject kwayland usage from here anymore

Test Plan: Dialogs still have shadows and still move under wayland

Reviewers: #plasma, graesslin

Reviewed By: #plasma, graesslin

Subscribers: graesslin, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D3024