Remove dart backend

test/dart_codegen/expect/core/int.dart

-part of dart.core;
- abstract class int extends num {external const factory int.fromEnvironment(String name, {
-  int defaultValue}
-);
- int operator &(int other);
- int operator |(int other);
- int operator ^(int other);
- int operator ~();
- int operator <<(int shiftAmount);
- int operator >>(int shiftAmount);
- bool get isEven;
- bool get isOdd;
- int get bitLength;
- int toUnsigned(int width);
- int toSigned(int width);
- int operator -();
- int abs();
- int get sign;
- int round();
- int floor();
- int ceil();
- int truncate();
- double roundToDouble();
- double floorToDouble();
- double ceilToDouble();
- double truncateToDouble();
- String toString();
- String toRadixString(int radix);
- external static int parse(String source, {
-  int radix, int onError(String source)}
-);
-}