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If you come across this post and are looking for an answer in Esri Javascript 4.0, try this:
view.ui.remove("attribution");
This will remove the widget from the ui of the view. In 4.0, the attibution widget is added by default.
Alternatively, you can specify the widgets you want created automatically in the default UI object when defining your view
See DefaultUI | API Reference | ArcGIS API for JavaScript 4.0
Fore more details.