Folded "DynamoViewModel.Exit" into "updateManager_ShutdownRequested"
RecordedTest/CodeBlockNodeTest do not need to "shutdown the host"
Removed unwanted argument from "DynamoModel.ShutDown" method
Updated signature of "ShutdownRequestedEventHandler" delegate
Merge pull request #2436 from Benglin/MinorCleanUp

Clean-up of DynamoModel.ShutDown methods