Remove package:unittest from some tests

tests/lib/math/point_test.dart

 // Copyright (c) 2013, 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.
 
 library point_test;
 
 import 'dart:math';
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 main() {
   test('constructor', () {
     var point = new Point(0, 0);
     expect(point.x, 0);
     expect(point.y, 0);
     expect('$point', 'Point(0, 0)');
   });
 
   test('constructor X', () {
@@ skipping 62 matching lines @@
   test('magnitute', () {
     var a = new Point(5, 10);
     var b = new Point(0, 0);
     expect(a.magnitude, a.distanceTo(b));
     expect(b.magnitude, 0);
 
     var c = new Point(-5, -10);
     expect(c.magnitude, a.distanceTo(b));
   });
 }