Remove deprecated mappedBy.

runtime/lib/array.dart

Index: runtime/lib/array.dart
diff --git a/runtime/lib/array.dart b/runtime/lib/array.dart
index 0f02eb4c01c30ff062241f0ecba9190cf985d55f..1441dc2a50e4b34a97de693994693f7f365f85ea 100644
--- a/runtime/lib/array.dart
+++ b/runtime/lib/array.dart
@@ -104,10 +104,6 @@ class _ObjectArray<E> implements List<E> {
     return IterableMixinWorkaround.mapList(this, f);
   }
 
-  List mappedBy(f(E element)) {
-    IterableMixinWorkaround.mappedByList(this, f);
-  }
-
   reduce(initialValue, combine(previousValue, E element)) {
     return IterableMixinWorkaround.reduce(this, initialValue, combine);
   }
@@ -338,10 +334,6 @@ class _ImmutableArray<E> implements List<E> {
     return IterableMixinWorkaround.mapList(this, f);
   }
 
-  List mappedBy(f(E element)) {
-    return IterableMixinWorkaround.mappedByList(this, f);
-  }
-
   String join([String separator]) {
     return IterableMixinWorkaround.joinList(this, separator);
   }