widget: Remove some leftovers

gtk_widget_can_activate_accel is gone, so remove the
vfunc and declaration.

docs/reference/gtk/gtk4-sections.txt

@@ -3971,7 +3971,6 @@ gtk_widget_allocate
 gtk_widget_class_add_shortcut
 gtk_widget_class_add_binding
 gtk_widget_class_add_binding_signal
-gtk_widget_can_activate_accel
 gtk_widget_activate
 gtk_widget_is_focus
 gtk_widget_grab_focus

gtk/gtkwidget.h

@@ -191,9 +191,6 @@ struct _GtkWidget
  * @keynav_failed: Signal emitted if keyboard navigation fails.
  * @get_accessible: Returns the accessible object that describes the
  *   widget to an assistive technology.
- * @can_activate_accel: Signal allows applications and derived widgets
- *   to override the default GtkWidget handling for determining whether
- *   an accelerator can be activated.
  * @query_tooltip: Signal emitted when “has-tooltip” is %TRUE and the
  *   hover timeout has expired with the cursor hovering “above”
  *   widget; or emitted when widget got focus in keyboard mode.
@@ -264,10 +261,6 @@ struct _GtkWidgetClass
    */
   AtkObject *  (* get_accessible)     (GtkWidget       *widget);
 
-  gboolean     (* can_activate_accel) (GtkWidget *widget,
-                                       guint      signal_id);
-
-
   gboolean     (* query_tooltip)      (GtkWidget  *widget,
                                        gint        x,
                                        gint        y,
@@ -398,9 +391,6 @@ void       gtk_widget_class_add_shortcut  (GtkWidgetClass      *widget_class,
                                            GtkShortcut         *shortcut);
 
 GDK_AVAILABLE_IN_ALL
-gboolean   gtk_widget_can_activate_accel  (GtkWidget           *widget,
-                                           guint                signal_id);
-GDK_AVAILABLE_IN_ALL
 gboolean   gtk_widget_mnemonic_activate   (GtkWidget           *widget,
                                            gboolean             group_cycling);
 GDK_AVAILABLE_IN_ALL