pkg/http: updated unittest dependency, removed unused imports

pkg/http/test/streamed_request_test.dart

Index: pkg/http/test/streamed_request_test.dart
diff --git a/pkg/http/test/streamed_request_test.dart b/pkg/http/test/streamed_request_test.dart
index afe8e098fcc56cbda28b249221fc92868dbc7237..444b36b3d248d3c3e438fec6cd5852ac78b37f77 100644
--- a/pkg/http/test/streamed_request_test.dart
+++ b/pkg/http/test/streamed_request_test.dart
@@ -4,8 +4,6 @@
 
 library streamed_request_test;
 
-import 'dart:convert';
-
 import 'package:http/http.dart' as http;
 import 'package:unittest/unittest.dart';
 
@@ -29,4 +27,4 @@ void main() {
       expect(() => request.contentLength = 10, throwsStateError);
     });
   });
-}
+}