Delete a bunch of packages that are now on GitHub.

pkg/http_multi_server/README.md

-An implementation of `dart:io`'s [HttpServer][] that wraps multiple servers and
-forwards methods to all of them. It's useful for serving the same application on
-multiple network interfaces while still having a unified way of controlling the
-servers. In particular, it supports serving on both the IPv4 and IPv6 loopback
-addresses using [HttpMultiServer.loopback][].
-
-```dart
-import 'package:http_multi_server/http_multi_server.dart';
-import 'package:shelf/shelf.dart' as shelf;
-import 'package:shelf/shelf_io.dart' as shelf_io;
-
-void main() {
-  // Both http://127.0.0.1:8080 and http://[::1]:8080 will be bound to the same
-  // server.
-  HttpMultiServer.loopback(8080).then((server) {
-    shelf_io.serveRequests(server, (request) {
-      return new shelf.Response.ok("Hello, world!");
-    });
-  });
-}
-```
-
-[HttpServer]: https://api.dartlang.org/apidocs/channels/stable/dartdoc-viewer/dart-io.HttpServer
-
-[HttpMultiServer.loopback]: https://api.dartlang.org/apidocs/channels/stable/dartdoc-viewer/http_multi_server/http_multi_server.HttpMultiServer#id_loopback