pkg/test: Remove unused imports

test/runner/timeout_test.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 @TestOn("vm")
 
-import 'dart:io';
-import 'dart:math' as math;
-
 import 'package:scheduled_test/descriptor.dart' as d;
-import 'package:scheduled_test/scheduled_stream.dart';
 import 'package:scheduled_test/scheduled_test.dart';
-import 'package:test/src/util/exit_codes.dart' as exit_codes;
 
 import '../io.dart';
 
 void main() {
   useSandbox();
 
   test("respects top-level @Timeout declarations", () {
     d.file("test.dart", '''
 @Timeout(const Duration(seconds: 0))
 
@@ skipping 58 matching lines @@
     // test to fail.
     var test = runTest(["--timeout=0.016x", "test.dart"]);
     test.stdout.expect(containsInOrder([
       "Test timed out after 0.4 seconds.",
       "-1: Some tests failed."
     ]));
     test.shouldExit(1);
   });
 }