Remove left touch border by default

The screen edge touch action causes this bug on X11: https://bugs.kde.org/show_bug.cgi?id=387775 Improvements to the touch edge action are blocked, as they would worsen this bug: !16 (closed) Since most Plasma users don't have a touchscreen computer, but they still are affected by this bug, it makes sense to disable the option by default until most users will be on Wayland, where there is no such problem.