unsubscribe method
Implementation
void unsubscribe(MethodCall call) {
var channelName = call.arguments['channelName'];
var channel = pusher!.channel(channelName);
pusher!.unsubscribe(channelName);
channel?.unbind_all();
}
void unsubscribe(MethodCall call) {
var channelName = call.arguments['channelName'];
var channel = pusher!.channel(channelName);
pusher!.unsubscribe(channelName);
channel?.unbind_all();
}