Fix analyzer hints and warnings in test/.

test/descriptor.dart

Index: test/descriptor.dart
diff --git a/test/descriptor.dart b/test/descriptor.dart
index 966a45aae2ee0165c96cf0f73e115374f1d8d431..5c65caefaad5e7cc70b80c75935463bcf2976627 100644
--- a/test/descriptor.dart
+++ b/test/descriptor.dart
@@ -5,16 +5,11 @@
 /// Pub-specific scheduled_test descriptors.
 library descriptor;
 
-import "dart:io" show File;
-
 import 'package:oauth2/oauth2.dart' as oauth2;
-import 'package:path/path.dart' as p;
 import 'package:pub/src/io.dart';
 import 'package:pub/src/utils.dart';
 import 'package:scheduled_test/descriptor.dart';
 import 'package:scheduled_test/scheduled_server.dart';
-import 'package:package_config/packages_file.dart' as packages_file;
-import 'package:stack_trace/stack_trace.dart';
 
 import 'descriptor/git.dart';
 import 'descriptor/tar.dart';