Make GtkEntry a no-window widget

Use input-only windows for capturing input, and just draw onto
the parent window. This allows themes to make entries with rounded
corners. Patch by Boram Park.

https://bugzilla.gnome.org/show_bug.cgi?id=632736

docs/reference/gtk/gtk3-sections.txt

@@ -1031,8 +1031,6 @@ gtk_entry_set_icon_tooltip_markup
 gtk_entry_get_icon_tooltip_markup
 gtk_entry_set_icon_drag_source
 gtk_entry_get_current_icon_drag_source
-gtk_entry_get_icon_window
-gtk_entry_get_text_window
 
 <SUBSECTION Standard>
 GTK_ENTRY