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/Tab.h

@@ -88,8 +88,6 @@ public:
     void set_user_agent_string(ByteString const&);
     void set_navigator_compatibility_mode(ByteString const&);
 
-    void set_preferred_languages(ReadonlySpan<String> preferred_languages);
-
     bool url_is_hidden() const { return m_location_edit->url_is_hidden(); }
     void set_url_is_hidden(bool url_is_hidden) { m_location_edit->set_url_is_hidden(url_is_hidden); }