[kcmkwin/kwinscreenedges] Disable left touch edge by default

On X11, it creates a dead pixel on the left edge which interferes with left panels, the left-nost widget on bottom and top panels, and scroll events on the left-most pixel in various apps.

It works properly on Wayland, but unfortunately turning it off by default only on X11 but not Wayland is not easily doable. So let's turn it off by default everywhere.

BUG: 387775 FIXED-IN: 5.21