ui: Excise old frames UI

This is no longer used, in favor of the standalone frames client.

Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/1077
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2175>

src/core/restart.c

@@ -42,7 +42,6 @@
 #include "core/display-private.h"
 #include "core/util-private.h"
 #include "meta/main.h"
-#include "ui/ui.h"
 #include "x11/meta-x11-display-private.h"
 
 static gboolean restart_helper_started = FALSE;