removing a circuit from a circuit breaker
Just turn it off and tape it so it stays off. Off does translate to completely dead and not even some stand-by power can be obtained. You never want to remove any wiring completely, regardless of your use or non-use...you don't know the future nor the future occupants. If you need the circuit for another new circuit, then your Electrician (not you) would just disconnect the old circuit from the breaker and run the new circuit.