windowManager: Drop AppSwitchAction

This gesture to switch the focused app was already a bit of a compromise solution at the time it was added, its clunky way to work (3fg long press, then taps with a 4th finger to switch application) was pretty much picking up the remains of our limited wiggle room (sticking to 3fg/4fg global gestures, since 2fg are application domain).

But then directional 3fg gestures took prevalence, and made it easier to switch between applications. This small gesture remained a bit of an easter egg, largely unused and unknown.

Fast forward to today, and it's being noticed in a bad way. The changes to event handling and delivery to actions has made this gesture take prevalence over the wee-bit-more-popular 3fg swipe gestures, making those never become active and never trigger.

While a gesture framework is being investigated that might help handle these situations (or, in a less undefined manner), this doesn't seem like a case worth going out of our way to hack around until that is in place. We can remove this, and make all WM interactions go through the 3fg directional gestures.

Closes: mutter#2729 (closed)