Remove some bogus type promotion code.

pkg/front_end/testcases/inference/type_promotion_not_and_not.dart

Index: pkg/front_end/testcases/inference/type_promotion_not_and_not.dart
diff --git a/pkg/front_end/testcases/inference/type_promotion_not_and_not.dart b/pkg/front_end/testcases/inference/type_promotion_not_and_not.dart
new file mode 100644
index 0000000000000000000000000000000000000000..69484a1cc07ae05eae69bd905641c825bd4c625e
--- /dev/null
+++ b/pkg/front_end/testcases/inference/type_promotion_not_and_not.dart
@@ -0,0 +1,14 @@
+// Copyright (c) 2017, 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.
+
+/*@testedFeatures=inference*/
+library test;
+
+void f(Object x) {
+  if (x is! int && x is! String) {
+    print(x);
+  }
+}
+
+main() {}