Remove DeviceEvent::Motion and WindowEvent::AxisMotion

We decided to remove them because they contained too little information
for the user to be useful. The assumption is that they were originally
implemented to enable gamepad support, which we already decided we are
not going to add directly to Winit.

examples/window.rs

@@ -488,7 +488,6 @@ impl ApplicationHandler for Application {
             | WindowEvent::HoveredFileCancelled
             | WindowEvent::KeyboardInput { .. }
             | WindowEvent::CursorEntered { .. }
-            | WindowEvent::AxisMotion { .. }
             | WindowEvent::DroppedFile(_)
             | WindowEvent::HoveredFile(_)
             | WindowEvent::Destroyed