Remove dart backend

test/dart_codegen/expect/async/async_error.dart

-part of dart.async;
- _invokeErrorHandler(Function errorHandler, Object error, StackTrace stackTrace) {
-  if (errorHandler is ZoneBinaryCallback) {
-    return errorHandler(error, stackTrace);
-    }
-   else {
-    return errorHandler(error);
-    }
-  }
- Function _registerErrorHandler(Function errorHandler, Zone zone) {
-  if (errorHandler is ZoneBinaryCallback) {
-    return zone.registerBinaryCallback(errorHandler);
-    }
-   else {
-    return zone.registerUnaryCallback(DEVC$RT.cast(errorHandler, Function, __CastType0, "ImplicitCast", """line 20, column 39 of dart:async/async_error.dart: """, errorHandler is __CastType0, true));
-    }
-  }
- class _UncaughtAsyncError extends AsyncError {_UncaughtAsyncError(error, StackTrace stackTrace) : super(error, _getBestStackTrace(error, stackTrace));
- static StackTrace _getBestStackTrace(error, StackTrace stackTrace) {
-  if (stackTrace != null) return stackTrace;
-   if (error is Error) {
-    return DEVC$RT.cast(error.stackTrace, dynamic, StackTrace, "DynamicCast", """line 31, column 14 of dart:async/async_error.dart: """, error.stackTrace is StackTrace, true);
-    }
-   return null;
-  }
- String toString() {
-  String result = "Uncaught Error: ${error}";
-   if (stackTrace != null) {
-    result += "\nStack Trace:\n$stackTrace";
-    }
-   return result;
-  }
-}
- typedef dynamic __CastType0(dynamic __u1);