Migrate many_generic_instanceof_test to language_2.

tests/language/many_generic_instanceof_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.
-// VMOptions=--optimization-counter-threshold=10 --no-background-compilation
-
-library GenericInstanceofTest.dart;
-
-import "package:expect/expect.dart";
-part "generic_instanceof.dart";
-
-class ManyGenericInstanceofTest {
-  static testMain() {
-    for (int i = 0; i < 20; i++) {
-      GenericInstanceof.testMain();
-    }
-  }
-}
-
-main() {
-  ManyGenericInstanceofTest.testMain();
-}