kcms/options: Hide "active mouse screen" option

In the late Plasma 5 times we agreed that it would be better to drop
"active mouse screen" option and stick with last interacted screen
approach instead. However, it was forgotten and nobody has pursued this
goal, so let's hide the option in the system settings ui at least.

The option is not completely removed because some parts of kwin would
need adjustments.


(cherry picked from commit e7d6e8b2)