Remove support for + prefix in number literals

tests/language/ternary_test.dart

 // Copyright (c) 2011, 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.
 // Dart test for testing the ternary operator.
 
 import "package:expect/expect.dart";
 
 class TernaryTest {
   static true_cond() { return true; }
   static false_cond() { return false; }
   static foo() { return -4; }
-  static moo() { return +5; }
+  static moo() { return 5; }
   static testMain() {
     Expect.equals(-4, (TernaryTest.true_cond() ? TernaryTest.foo()
                                                : TernaryTest.moo()));
-    Expect.equals(+5, (TernaryTest.false_cond() ? TernaryTest.foo()
+    Expect.equals(5, (TernaryTest.false_cond() ? TernaryTest.foo()
                                                 : TernaryTest.moo()));
   }
 }
 
 main() {
   TernaryTest.testMain();
 }