Do not install another set of listeners on _every_ sim reset.
Also improve performance by removing a listener for a property which is
written in _every_ loop anyway (don't waste another Nasal context).
(Do we really need a _Nasal_ loop running at full speed just to convert
a bunch of properties? It increases the load on the Nasal GC and
is unconditionally active, even if all shaders are disabled etc).
