LibGUI+WindowServer: Remove now-obsolete cursor tracking feature

This feature was problematic for several reasons:
- Tracking *all* the user activity seems like a privacy nightmare.
- LibGUI actually only supports one globally tracking widget per window,
  even if no window is necessary, or if multiple callbacks are desired.
- Widgets can easily get confused whether an event is actually directed
  at it, or is actually just the result of global tracking.

The third item caused an issue where right-clicking CatDog opened two
context menus instead of one.

Userland/Libraries/LibGUI/Widget.h

@@ -223,9 +223,6 @@ public:
     void set_font_weight(unsigned);
     void set_font_fixed_width(bool);
 
-    void set_global_cursor_tracking(bool);
-    bool global_cursor_tracking() const;
-
     void notify_layout_changed(Badge<Layout>);
     void invalidate_layout();