[kcm/kwinrules] Fix layout misalignment of list items

Summary:
Remove anchors within `Kirigami.AbstractListItem` delegates.
They were causing random misalignment of items in the main and the overlay `ListView`s

Test Plan:
Before {F8284332}
After {F8284333}

Reviewers: broulik, #vdg, #kwin, ngraham

Reviewed By: #vdg, ngraham

Subscribers: ahiemstra, ngraham, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D29423