http: remove unused variable in _http_server.js

PR-URL: https://github.com/nodejs/node/pull/26407
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_http_server.js

@@ -307,7 +307,6 @@ function Server(options, requestListener) {
 
   this.timeout = 2 * 60 * 1000;
   this.keepAliveTimeout = 5000;
-  this._pendingResponseData = 0;
   this.maxHeadersCount = null;
   this.headersTimeout = 40 * 1000; // 40 seconds
 }