stream: cleanup() when unpiping all streams.

This PR makes sure the object emitted as the 'unpipe'
event in the destination stream is not shared between
destination, as it would be muted.

Refs: https://github.com/nodejs/node/pull/12746
PR-URL: https://github.com/nodejs/node/pull/18266


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>