Remove obsolete http_base package

dart/pkg/http_base/lib/http_base_io.dart

-library http_base.http_base_io;
-
-import 'dart:io' as io;
-import 'dart:async';
-
-import 'http_base.dart';
-export 'http_base.dart';
-
-/// An implementation for [RequestHandler]. It uses dart:io to make http
-/// requests.
-class Client {
-  // TODO: Should we provide a mechanism to close (forcefully or not) [_client]?
-  final io.HttpClient _client = new io.HttpClient();
-
-  Future<Response> call(Request request) {
-   return _client.openUrl(request.method, request.url).then((ioRequest) {
-     // TODO: Special case Cookie/Set-Cookie here!
-
-     for (var name in request.headers.names) {
-       ioRequest.headers.set(name, request.headers[name]);
-     }
-
-     var stream = request.read();
-     return ioRequest.addStream(stream).then((_) {
-       return ioRequest.close();
-     });
-   }).then((io.HttpClientResponse ioResponse) {
-     var headerMap = {};
-     ioResponse.headers.forEach((name, values) {
-       headerMap[name] = values;
-     });
-     var headers = new HeadersImpl(headerMap);
-
-     return new ResponseImpl(
-         ioResponse.statusCode, headers: headers, body: ioResponse);
-   });
-  }
-}