refactor: about page as a widget

src/app/cosmic.rs

@@ -78,9 +78,6 @@ pub enum Message {
     /// Tracks updates to window suggested size.
     #[cfg(feature = "applet")]
     SuggestedBounds(Option<iced::Size>),
-    #[cfg(feature = "desktop")]
-    /// Opens the provided URL.
-    OpenUrl(String),
 }
 
 #[derive(Default)]
@@ -664,11 +661,6 @@ impl<T: Application> Cosmic<T> {
                 let core = self.app.core_mut();
                 core.applet.suggested_bounds = b;
             }
-            #[cfg(feature = "desktop")]
-            Message::OpenUrl(url) => match open::that_detached(url) {
-                Ok(_) => (),
-                Err(err) => tracing::error!("{err}"),
-            },
             _ => {}
         }