Mohan,
The GenerateRendererTask is limited by the requirement:
The GenerateRendererTask is available for map service or tables that support the generateDataClasses operation (version 10.1 or greater)
Your FeatureLayer is coming from a FeatureCollection and not a Map Service so it will not work.
So you just need to setup the ClassBreaksRenderer manually like in this sample:
Class breaks renderer | ArcGIS API for JavaScript 3.22