Revert "Make EfficientLength extend Iterable."

tests/language/efficient_length_warning_test.dart

Index: tests/language/efficient_length_warning_test.dart
diff --git a/tests/language/efficient_length_warning_test.dart b/tests/language/efficient_length_warning_test.dart
deleted file mode 100644
index aebce61cbec164b33988c3e602b2a18fc511b389..0000000000000000000000000000000000000000
--- a/tests/language/efficient_length_warning_test.dart
+++ /dev/null
@@ -1,15 +0,0 @@
-// 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.
-// Third dart test program.
-
-main(args) {
-  // This should no longer cause a warning because the least-upper-bound
-  // of List<int> and Set<int> is Object.
-  // The LUB is now EfficientLengthIterable and it extends Iterable.
-  var x = (args.length.isEven // Unpredictable condition.
-      ? <int>[1]
-      : new Set<int>.from([1])).first;
-  if (x != 1) throw "Wat?";
-}
-