Remove support for remaining deprecated features.

tests/language/unsupported_operators_test.dart

+// Copyright (c) 2013, 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.
+
+// Test handling of unsupported operators.
+
+library unsupported_operators;
+
+class C {
+  m() {
+    print(
+          super === /// 01: compile-time error
+          null);
+    print(
+          super !== /// 02: compile-time error
+          null);
+  }
+}
+
+void main() {
+  new C().m();
+  new C().m();
+  print(
+        "foo" === /// 03: compile-time error
+        null);
+  print(
+        "foo" !== /// 04: compile-time error
+        null);
+}