Stop listening for exit messages from the isolate.
Requests for the isolate to not send exit messages on responsePort.
If the isolate isn't expecting to send exit messages on responsePort,
because the port hasn't been added using addOnExitListener,
or because it has already been removed, the request is ignored.
If the same port has been passed via addOnExitListener more than once,
only one call to removeOnExitListener is needed to stop it from receiving
exit messagees.
Closing the receive port at the end of the send port will not stop the isolate from sending exit messages, they are just going to be lost.
An exit message may still be sent if the isolate terminates before this request is received and processed.
Source
external void removeOnExitListener(SendPort responsePort);