wayland: upgrade wayland-window (#339)

* wayland: upgrade wayland-window

This new version of wayland window considerably simplifies the
window handling for winit, meaning much of the previous juggling
is no longer needed, and the windows will appear even if nothing is
drawn.

* wayland: cleanup unused stuff

examples/multiwindow.rs

@@ -9,12 +9,6 @@ fn main() {
 
     let mut num_windows = 3;
 
-    if cfg!(target_os = "linux") {
-        println!("Running this example under wayland may not display a window at all.\n\
-                  This is normal and because this example does not actually draw anything in the window,\
-                  thus the compositor does not display it.");
-    }
-
     events_loop.run_forever(|event| {
         match event {
             winit::Event::WindowEvent { event: winit::WindowEvent::Closed, window_id } => {