Remove signature classes from the VM.

tests/language/regress_24567_test.dart

 // Copyright (c) 2016, 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.
 
 import "package:expect/expect.dart";
+import 'dart:math' as math;
 
-class C<D> {
-  void set D(int value) {
-    field = value;
-  }
+class Random { }
 
-  int field;
-}
+typedef F(Random r);
 
 main() {
-  C<int> c = new C<int>();
-  c.D = 1;
-  Expect.equals(c.field, 1);
+  f(Random r) { }
+  g(math.Random r) { }
+  Expect.isTrue(f is F);
+  Expect.isFalse(g is F);
 }