Remove dart backend

test/dart_codegen/expect/core/regexp.dart

-part of dart.core;
- abstract class Match {int get start;
- int get end;
- String group(int group);
- String operator [](int group);
- List<String> groups(List<int> groupIndices);
- int get groupCount;
- String get input;
- Pattern get pattern;
-}
- abstract class RegExp implements Pattern {external factory RegExp(String source, {
-bool multiLine : false, bool caseSensitive : true}
-);
- Match firstMatch(String input);
- Iterable<Match> allMatches(String input, [int start = 0]);
- bool hasMatch(String input);
- String stringMatch(String input);
- String get pattern;
- bool get isMultiLine;
- bool get isCaseSensitive;
-}