Remove documentation about "pub run test:test".

lib/src/executable.dart

 // Copyright (c) 2015, 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.
 
 // TODO(nweiz): This is under lib so that it can be used by the unittest dummy
 // package. Once that package is no longer being updated, move this back into
 // bin.
 import 'dart:io';
 
 import 'package:source_span/source_span.dart';
@@ skipping 164 matching lines @@
   var output = stdout;
 
   var message = "Runs tests in this package.";
   if (error != null) {
     message = error;
     output = stderr;
   }
 
   output.write("""${wordWrap(message)}
 
-Usage: pub run test:test [files or directories...]
+Usage: pub run test [files or directories...]
 
 ${Configuration.usage}
 """);
 }