Fix CI warnings (#1898)

* Fix CI warnings

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

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)>>,