[minor] Remove unneeded if statement

The `'error'` event can be emitted after the `'close'` event only if
`socket.write()` is called on a closed socket. If this happens, it's
a bug.

Author: lpinca

lib/websocket.js

@@ -893,8 +893,6 @@ function socketOnError() {
   this.removeListener('error', socketOnError);
   this.on('error', NOOP);
 
-  if (websocket) {
-    websocket.readyState = WebSocket.CLOSING;
-    this.destroy();
-  }
+  websocket.readyState = WebSocket.CLOSING;
+  this.destroy();
 }