Switch to downloaded SDK executable, drop executables in testing/bin.

tools/testing/dart/co19_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.
 
 /**
  * Tool for running co19 tests. Used when updating co19.
  *
  * Currently, this tool is merely a convenience around multiple
  * invocations of test.dart. Long term, we hope to evolve this into a
  * script that can automate most of the tasks necessary when updating
  * co19.
  *
  * Usage:
- * [: ./tools/testing/bin/$OS/dart tools/testing/dart/co19_test.dart :]
+ * [: dart tools/testing/dart/co19_test.dart :]
  */
 
 library co19_test;
 
 import "dart:io";
 
 import "test_options.dart";
 import "test_suite.dart";
 import "test_configurations.dart";
 
@@ skipping 24 matching lines @@
     arguments.addAll(args);
     arguments.addAll(commandLine);
     configurations.addAll(optionsParser.parse(arguments));
   }
 
   if (configurations != null || configurations.length > 0) {
     testConfigurations(configurations);
   }
 }