[kconf_update] Use scripted dim screen effect

Summary:
I forgot to add a kconf update that moves existing users of the builtin
Dim Screen effect to the scripted version of the effect, sorry.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16957

kconf_update/kwin.upd

@@ -19,3 +19,9 @@ Group=Effect-Scale,Effect-kwin4_effect_scale
 AllKeys
 Group=Plugins
 Key=scaleEnabled,kwin4_effect_scaleEnabled
+
+# Port the Dim Screen effect to JavaScript.
+Id=port-dimscreen-effect-to-js
+File=kwinrc
+Group=Plugins
+Key=dimscreenEnabled,kwin4_effect_dimscreenEnabled