deregisterChild(child) {
        if (this.controller.isInitialized) {
            throw new Error("Children may only be deregistered while the MQTT controller is not initialized");
        }

        const idx = this.children.indexOf(child);
        if (idx >= 0) {
            this.children.splice(idx, 1);
        }
    }
Deregister child.
This function must be used as a callback of the controller's reconfigure method so that the state is updated
accordingly.

@protected
@param {MqttHandle} child
@return {void}