I would like to know the inbuilt standards in puremvc to remove event listeners and unwatch the binding on all mediators, proxies and views which are not going to be in use any more coz of switch of views in the app.
There shouldn't be any bindings to Mediators or Proxies. They are retrieved as needed from the View and Model respectively and should not be referenced by view components or binding therein.
As for when to remove event listeners, that's up to you and the lifecycle of your component. However, it is typical that if a view component may be removed from the display list, that you set a listener in onRegister which listens for an event from the component indicating it has been removed. If you're using Flash, this would be Event.REMOVED_FROM_STAGE. In your handler for that, you may simply have the Mediator remove itself.