Remove dart backend

test/dart_codegen/expect/core/map.dart

-part of dart.core;
- abstract class Map<K, V> {factory Map() = LinkedHashMap<K, V>;
- factory Map.from(Map other) = LinkedHashMap<K, V>.from;
- factory Map.identity() = LinkedHashMap<K, V>.identity;
- factory Map.fromIterable(Iterable iterable, {
-  K key(element), V value(element)}
-) = LinkedHashMap<K, V>.fromIterable;
- factory Map.fromIterables(Iterable<K> keys, Iterable<V> values) = LinkedHashMap<K, V>.fromIterables;
- bool containsValue(Object value);
- bool containsKey(Object key);
- V operator [](Object key);
- void operator []=(K key, V value);
- V putIfAbsent(K key, V ifAbsent());
- void addAll(Map<K, V> other);
- V remove(Object key);
- void clear();
- void forEach(void f(K key, V value));
- Iterable<K> get keys;
- Iterable<V> get values;
- int get length;
- bool get isEmpty;
- bool get isNotEmpty;
-}