kcmkwin/kwinscreenedges: only show touch screen edges KCM on Wayland
The touch screen edge features that this KCM lets you trigger barely work on X11 and really only work properly on Wayland.
Unfortunately we don't have the ability to have separate settings between X11 and Wayland, and for this reason we removed a default left touch edge in 3df79855 a year and a half ago because it was too buggy on X11.
This commit takes the next step and hides the KCM entirely on X11, so you can only use it on Wayland where it actually works properly.
One potential downside is be that any users who are actually using it on X11 will lose the ability to use a GUI to configure these features unless they go to the Wayland session to do it. However the number of such users is likely small given how the feature does not really work on X11.
However the upside is that Wayland users who can see the KCM can actually use the features that it lets you configure because they work properly there.