Fix CI warnings (#1898)

* Fix CI warnings

* Use the panic! macro rather than format! + panic_any

src/platform_impl/web/stdweb/canvas.rs

@@ -17,6 +17,7 @@ use stdweb::web::event::{
 use stdweb::web::html_element::CanvasElement;
 use stdweb::web::{document, EventListenerHandle, IElement, IEventTarget, IHtmlElement};
 
+#[allow(dead_code)]
 pub struct Canvas {
     /// Note: resizing the CanvasElement should go through `backend::set_canvas_size` to ensure the DPI factor is maintained.
     raw: CanvasElement,

src/platform_impl/web/web_sys/canvas.rs

@@ -18,6 +18,7 @@ use web_sys::{
 mod mouse_handler;
 mod pointer_handler;
 
+#[allow(dead_code)]
 pub struct Canvas {
     common: Common,
     on_focus: Option<EventListenerHandle<dyn FnMut(FocusEvent)>>,

src/platform_impl/web/web_sys/canvas/mouse_handler.rs

@@ -8,6 +8,7 @@ use std::rc::Rc;
 
 use web_sys::{EventTarget, MouseEvent};
 
+#[allow(dead_code)]
 pub(super) struct MouseHandler {
     on_mouse_leave: Option<EventListenerHandle<dyn FnMut(MouseEvent)>>,
     on_mouse_enter: Option<EventListenerHandle<dyn FnMut(MouseEvent)>>,

src/platform_impl/web/web_sys/canvas/pointer_handler.rs

@@ -5,6 +5,7 @@ use crate::event::{ModifiersState, MouseButton};
 
 use web_sys::PointerEvent;
 
+#[allow(dead_code)]
 pub(super) struct PointerHandler {
     on_cursor_leave: Option<EventListenerHandle<dyn FnMut(PointerEvent)>>,
     on_cursor_enter: Option<EventListenerHandle<dyn FnMut(PointerEvent)>>,