Remove pressedButtons, now implemented via MouseTracker (#302)

Author: hamoid

orx-view-box/src/commonMain/kotlin/ViewBox.kt

@@ -56,8 +56,10 @@ class ViewBox(
         override val moved = Event<MouseEvent>()
         override var position: Vector2 = -clientArea.corner
 
-        override val pressedButtons: MutableSet<MouseButton>
-            get() = TODO("Not yet implemented")
+        // Note: use MouseTracker() instead of pressedButtons
+        //override val pressedButtons: MutableSet<MouseButton>
+        //    get() = TODO("Not yet implemented")
+
         override val scrolled = Event<MouseEvent>()
     }
 
@@ -298,4 +300,4 @@ fun Program.viewBox(
         viewBox.f()
     }
     return viewBox
-}
+}