Ladybird: Remove the "home" icon from the toolbar (and the concept)

This feature isn't really that useful in practice, so let's remove it.
(Other browsers haven't had this action for years either.)

Ladybird/SettingsDialog.h

@@ -24,7 +24,6 @@ public:
 private:
     QFormLayout* m_layout;
     QPushButton* m_ok_button { nullptr };
-    QLineEdit* m_homepage { nullptr };
     QLineEdit* m_new_tab_page { nullptr };
     QMainWindow* m_window { nullptr };
 };