[kcmkwin/compositing] Use new icon for Effects KCM

Summary: Use the new icon introduced in D18457

Test Plan: {F6563102}

Reviewers: #vdg, davidedmundson, GB_2

Reviewed By: #vdg, davidedmundson, GB_2

Subscribers: Codezela, GB_2, zzag, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D18461