Don't set serverHeader by default.

sdk/lib/io/http.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 /**
  * HTTP status codes.
  */
 abstract class HttpStatus {
@@ skipping 66 matching lines @@
  *
  *     HttpServer.bind(InternetAddress.ANY_IP_V6, 80).then((server) {
  *       server.listen((HttpRequest request) {
  *         // Handle requests.
  *       });
  *     });
  */
 abstract class HttpServer implements Stream<HttpRequest> {
   /**
    * Set and get the default value of the `Server` header for all responses
-   * generated by this [HttpServer]. The default value is
-   * `Dart/<version> (dart:io)`.
+   * generated by this [HttpServer]. By default, it's disabled.
    *
    * If the serverHeader is set to `null`, no default `Server` header will be
    * added to each response.
    */
   String serverHeader;
 
   /**
    * Get or set the timeout used for idle keep-alive connections. If no further
    * request is seen within [idleTimeout] after the previous request was
    * completed, the connection is dropped.
@@ skipping 1513 matching lines @@
 class RedirectException implements HttpException {
   final String message;
   final List<RedirectInfo> redirects;
 
   const RedirectException(this.message, this.redirects);
 
   String toString() => "RedirectException: $message";
 
   Uri get uri => redirects.last.location;
 }