fix: simplify the check for WebSocket availability

This check was added for the flashsocket transport, which has been
deprecated for a while now ([1]). But it fails with latest webpack
versions, as the expression `"__initialize" in WebSocket` gets
evaluated to `true`.

Related:

- #689
- socketio/socket.io-client#1537

[1]: dbc65f3

lib/transports/websocket.ts

@@ -240,9 +240,6 @@ export class WS extends Transport {
    * @api public
    */
   check() {
-    return (
-      !!WebSocket &&
-      !("__initialize" in WebSocket && this.name === WS.prototype.name)
-    );
+    return !!WebSocket;
   }
 }