[gtk] StyleContext: Don't advise using invalidate()

[Daniel Boles <dboles src gnome org>]

commit acd05d09aa24444c0df2742668845c44aed3cb3e
Author: Daniel Boles <dboles src gmail com>
Date:   Mon May 21 23:38:54 2018 +0100

    StyleContext: Don't advise using invalidate()
    
    It doesn't exist anymore! Also, set_display() is not needed/used in the
    demo cited, and we were still referring to gtk3-demo, not gtk4-demo.

 gtk/gtkstylecontext.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)
---
diff --git a/gtk/gtkstylecontext.c b/gtk/gtkstylecontext.c
index 54eca205f1..53888073f5 100644
--- a/gtk/gtkstylecontext.c
+++ b/gtk/gtkstylecontext.c
@@ -73,11 +73,8 @@
  *
  * If you are using the theming layer standalone, you will need to set a
  * widget path and a display yourself to the created style context through
- * gtk_style_context_set_path() and gtk_style_context_set_display(), as well
- * as updating the context yourself using gtk_style_context_invalidate()
- * whenever any of the conditions change, such as a change in the
- * #GtkSettings:gtk-theme-name setting or a hierarchy change in the rendered
- * widget. See the “Foreign drawing“ example in gtk3-demo.
+ * gtk_style_context_set_path() and possibly gtk_style_context_set_display().
+ * See the “Foreign drawing“ example in gtk4-demo.
  *
  * # Style Classes # {#gtkstylecontext-classes}
  *