styleprovider: Deprecate two non-working functions

Both of them weren't used inside GTK. And apparently they weren't used
outside of GTK either, as alex recently mentioned them being severly
broken.

gtk/gtkstyleprovider.c

@@ -66,6 +66,9 @@ gtk_style_provider_iface_init (gpointer g_iface)
  * style settings affecting @path
  *
  * Since: 3.0
+ *
+ * Deprecated: 3.8: Will always return %NULL for all GTK-provided style providers
+ *     as the interface cannot correctly work the way CSS is specified.
  **/
 GtkStyleProperties *
 gtk_style_provider_get_style (GtkStyleProvider *provider,
@@ -132,6 +135,8 @@ gtk_style_provider_get_style_property (GtkStyleProvider *provider,
  * Returns: (transfer none): The icon factory to use for @path, or %NULL
  *
  * Since: 3.0
+ *
+ * Deprecated: 3.8: Will always return %NULL for all GTK-provided style providers.
  **/
 GtkIconFactory *
 gtk_style_provider_get_icon_factory (GtkStyleProvider *provider,

gtk/gtkstyleprovider.h

@@ -109,6 +109,7 @@ struct _GtkStyleProviderIface
 
 GType gtk_style_provider_get_type (void) G_GNUC_CONST;
 
+GDK_DEPRECATED_IN_3_8
 GtkStyleProperties *gtk_style_provider_get_style (GtkStyleProvider *provider,
                                                   GtkWidgetPath    *path);
 
@@ -118,6 +119,7 @@ gboolean gtk_style_provider_get_style_property (GtkStyleProvider *provider,
                                                 GParamSpec       *pspec,
                                                 GValue           *value);
 
+GDK_DEPRECATED_IN_3_8_FOR(NULL)
 GtkIconFactory * gtk_style_provider_get_icon_factory (GtkStyleProvider *provider,
 						      GtkWidgetPath    *path);