gtk/: fully remove gtkalias hacks

https://bugzilla.gnome.org/show_bug.cgi?id=623845

gtk/gtkassistant.c

@@ -64,8 +64,6 @@
 #include "gtkprivate.h"
 #include "gtkbuildable.h"
 
-#include "gtkalias.h"
-
 #define GTK_ASSISTANT_GET_PRIVATE(o) (G_TYPE_INSTANCE_GET_PRIVATE ((o), GTK_TYPE_ASSISTANT, GtkAssistantPrivate))
 
 #define HEADER_SPACING 12
@@ -2551,7 +2549,3 @@ gtk_assistant_buildable_custom_finished (GtkBuildable *buildable,
   parent_buildable_iface->custom_finished (buildable, builder, child,
                                            tagname, user_data);
 }
-
-
-#define __GTK_ASSISTANT_C__
-#include "gtkaliasdef.c"