function compareNumber(a, b) {
  return b - a;
}
Unregisters a previously registered callback.

@param {Listener} listener The function to be unregistered.
@param {object} [scope] The scope that was originally passed to addEventListener.
@returns {boolean} <code>true</code> if the listener was removed; <code>false</code> if the listener and scope are not registered with the event.

@see Event#addEventListener
@see Event#raiseEvent