pkg/http: updated unittest dependency, removed unused imports

pkg/http/test/html/streamed_request_test.dart

Index: pkg/http/test/html/streamed_request_test.dart
diff --git a/pkg/http/test/html/streamed_request_test.dart b/pkg/http/test/html/streamed_request_test.dart
index e75d130e00fa4ce29220a09da57632e9a6a9f3bc..907bcaffee2db90ef1c8128a27b92b5233d867fe 100644
--- a/pkg/http/test/html/streamed_request_test.dart
+++ b/pkg/http/test/html/streamed_request_test.dart
@@ -4,8 +4,6 @@
 
 library http.test.html.streamed_request_test;
 
-import 'dart:convert';
-
 import 'package:http/http.dart' as http;
 import 'package:http/browser_client.dart';
 import 'package:unittest/unittest.dart';
@@ -37,4 +35,4 @@ void main() {
       });
     });
   });
-}
+}