Remove dart backend

test/dart_codegen/expect/collection/hash_map.dart

-part of dart.collection;
- bool _defaultEquals(Object a, Object b) => a == b;
- int _defaultHashCode(Object a) => a.hashCode;
- typedef bool _Equality<K>(K a, K b);
- typedef int _Hasher<K>(K object);
- abstract class HashMap<K, V> implements Map<K, V> {external factory HashMap({
-  bool equals(K key1, K key2), int hashCode(K key), bool isValidKey(potentialKey)}
-);
- external factory HashMap.identity();
- factory HashMap.from(Map other) {
-  HashMap<K, V> result = new HashMap<K, V>();
-   other.forEach((k, v) {
-    result[DEVC$RT.cast(k, dynamic, K, "CompositeCast", """line 87, column 35 of dart:collection/hash_map.dart: """, k is K, false)] = DEVC$RT.cast(v, dynamic, V, "CompositeCast", """line 87, column 40 of dart:collection/hash_map.dart: """, v is V, false);
-    }
-  );
-   return result;
-  }
- factory HashMap.fromIterable(Iterable iterable, {
-  K key(element), V value(element)}
-) {
-  HashMap<K, V> map = new HashMap<K, V>();
-   Maps._fillMapWithMappedIterable(map, iterable, key, value);
-   return map;
-  }
- factory HashMap.fromIterables(Iterable<K> keys, Iterable<V> values) {
-  HashMap<K, V> map = new HashMap<K, V>();
-   Maps._fillMapWithIterables(map, keys, values);
-   return map;
-  }
-}