The callback would schedule a clutter_actor_destroy() on the first
argument. Unless told otherwise, this is the same actor that is
already being destroyed, so this is a no-op.
Instead, the intent is to make the clone follow up destruction of
the window actor so that it results in correct removal of this
window from the ShellWindowPreviewLayout. Use a swapped connection
to pass the clone actor as the first argument of the signal callback.
Fixes: 04c781674c ("Move WindowPreviewLayout from JS to C")
Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6570
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2756>
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