gtk: Drop gtk_widget_get_modifier_mask

This is not used anymore.

docs/reference/gtk/gtk4-sections.txt

@@ -4063,7 +4063,6 @@ gtk_widget_get_support_multidevice
 gtk_widget_get_realized
 gtk_widget_get_mapped
 gtk_widget_device_is_shadowed
-gtk_widget_get_modifier_mask
 gtk_widget_get_opacity
 gtk_widget_set_opacity
 gtk_widget_get_overflow

gtk/gtkwidget.c

@@ -10662,27 +10662,6 @@ gtk_widget_get_style_context (GtkWidget *widget)
   return priv->context;
 }
 
-/**
- * gtk_widget_get_modifier_mask:
- * @widget: a #GtkWidget
- * @intent: the use case for the modifier mask
- *
- * Returns the modifier mask the @widget’s windowing system backend
- * uses for a particular purpose.
- *
- * See gdk_display_get_modifier_mask().
- *
- * Returns: the modifier mask used for @intent.
- **/
-GdkModifierType
-gtk_widget_get_modifier_mask (GtkWidget         *widget,
-                              GdkModifierIntent  intent)
-{
-  g_return_val_if_fail (GTK_IS_WIDGET (widget), 0);
-
-  return gdk_display_get_modifier_mask (_gtk_widget_get_display (widget), intent);
-}
-
 static GtkActionMuxer *
 gtk_widget_get_parent_muxer (GtkWidget *widget,
                              gboolean   create)

gtk/gtkwidget.h

@@ -771,10 +771,6 @@ void              gtk_widget_class_set_css_name (GtkWidgetClass *widget_class,
 GDK_AVAILABLE_IN_ALL
 const char *      gtk_widget_class_get_css_name (GtkWidgetClass *widget_class);
 
-GDK_AVAILABLE_IN_ALL
-GdkModifierType   gtk_widget_get_modifier_mask (GtkWidget         *widget,
-                                                GdkModifierIntent  intent);
-
 GDK_AVAILABLE_IN_ALL
 guint gtk_widget_add_tick_callback (GtkWidget       *widget,
                                     GtkTickCallback  callback,