Remove dart backend

test/dart_codegen/expect/async/timer.dart

-part of dart.async;
- abstract class Timer {factory Timer(Duration duration, void callback()) {
-  if (Zone.current == Zone.ROOT) {
-    return Zone.current.createTimer(duration, callback);
-    }
-   return Zone.current.createTimer(duration, Zone.current.bindCallback(callback, runGuarded: true));
-  }
- factory Timer.periodic(Duration duration, void callback(Timer timer)) {
-  if (Zone.current == Zone.ROOT) {
-    return Zone.current.createPeriodicTimer(duration, callback);
-    }
-   return Zone.current.createPeriodicTimer(duration, ((__x78) => DEVC$RT.cast(__x78, ZoneUnaryCallback, __CastType76, "CompositeCast", """line 80, column 19 of dart:async/timer.dart: """, __x78 is __CastType76, false))(Zone.current.bindUnaryCallback(callback, runGuarded: true)));
-  }
- static void run(void callback()) {
-  new Timer(Duration.ZERO, callback);
-  }
- void cancel();
- bool get isActive;
- external static Timer _createTimer(Duration duration, void callback());
- external static Timer _createPeriodicTimer(Duration duration, void callback(Timer timer));
-}
- typedef void __CastType76(Timer __u77);