remove implicit once

websockets#1754 (comment)

lib/event-target.js

@@ -116,26 +116,22 @@ const EventTarget = {
    */
   addEventListener(method, listener, options = {}) {
     if (typeof listener !== 'function') return;
-    const { once } = options;
 
     function onMessage(data) {
       listener.call(this, new MessageEvent(data, this));
-      if (once) this.removeListener(method, listener);
+      if (options.once) this.removeListener(method, listener);
     }
 
     function onClose(code, message) {
       listener.call(this, new CloseEvent(code, message, this));
-      if (once) this.removeListener(method, listener);
     }
 
     function onError(error) {
       listener.call(this, new ErrorEvent(error, this));
-      if (once) this.removeListener(method, listener);
     }
 
     function onOpen() {
       listener.call(this, new OpenEvent(this));
-      if (once) this.removeListener(method, listener);
     }
 
     if (method === 'message') {