Revert "Make EfficientLength extend Iterable."

sdk/lib/core/list.dart

Index: sdk/lib/core/list.dart
diff --git a/sdk/lib/core/list.dart b/sdk/lib/core/list.dart
index 33e011c09060163842f50a29bc71da1824ebeb98..d887e67600a65f636475b4d758f136eb93977ece 100644
--- a/sdk/lib/core/list.dart
+++ b/sdk/lib/core/list.dart
@@ -51,7 +51,7 @@ part of dart.core;
  * directly or through iterating an [Iterable] that is backed by the list, will
  * break the iteration.
  */
-abstract class List<E> implements EfficientLengthIterable<E> {
+abstract class List<E> implements Iterable<E>, EfficientLength {
   /**
    * Creates a list of the given length.
    *