LibWeb+LibWebView+UI: Migrate to LibWebView's language settings

Author: https://github.com/trflynn89
Commit: a3ea4881e7
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4215
Reviewed-by: https://github.com/gmta ✅

UI/Qt/BrowserWindow.h

@@ -24,7 +24,6 @@
 
 namespace Ladybird {
 
-class SettingsDialog;
 class WebContentView;
 
 class BrowserWindow : public QMainWindow {
@@ -210,8 +209,6 @@ private:
     ByteString m_user_agent_string {};
     ByteString m_navigator_compatibility_mode {};
 
-    SettingsDialog* m_settings_dialog { nullptr };
-
     IsPopupWindow m_is_popup_window { IsPopupWindow::No };
 };