Fix --strong warnings in pkg/fixnum

pkg/fixnum/test/int_32_test.dart

 // Copyright (c) 2012, 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 Int32test;
 import 'package:fixnum/fixnum.dart';
 import 'package:unittest/unittest.dart';
 
 void main() {
   group("isX tests", () {
@@ skipping 38 matching lines @@
       expect(Int32.MAX_VALUE.bitLength, 31);
       expect(Int32.MIN_VALUE.bitLength, 31);
     });
   });
 
   group("arithmetic operators", () {
     Int32 n1 = new Int32(1234);
     Int32 n2 = new Int32(9876);
     Int32 n3 = new Int32(-1234);
     Int32 n4 = new Int32(-9876);
-    Int32 n5 = new Int32(0x12345678);
-    Int32 n6 = new Int32(0x22222222);
 
     test("+", () {
       expect(n1 + n2, new Int32(11110));
       expect(n3 + n2, new Int32(8642));
       expect(n3 + n4, new Int32(-11110));
       expect(Int32.MAX_VALUE + 1, Int32.MIN_VALUE);
       expect(() => new Int32(17) + null, throws);
     });
 
     test("-", () {
@@ skipping 287 matching lines @@
       expect(new Int32(-1).shiftRightUnsigned(8).toHexString(), "ffffff");
     });
   });
 
   group("toRadixString", () {
     test("returns base n string representation", () {
       expect(new Int32(123456789).toRadixString(5), "223101104124");
     });
   });
 }