can you elaborate on what you mean by a risk charter and 'deleting'?
in general you 'retire' a risk through mitigation and state in you documentation that the failure mode has been eliminated but you maintain the historical record of it's existence and what you did about it.
No, it's a good practice to keep every identified and controlled risk. For example, if you change the device or software afterwards, you are required to verify if there's any new risks or if already controlled risks were modified (it may be the case the the original controlled risk is not controlled anymore).