chore: disable dart for HTTP package

BREAKING CHANGE

Stop supporting http module in Dart. This is because Dart has a
well developed http package which should be used by Dart
customers instead.

gulpfile.js

@@ -621,7 +621,7 @@ gulp.task('test.unit.dart', function (done) {
         return;
       }
 
-      watch(['modules/angular2/**', 'modules/http/**'], { ignoreInitial: true }, [
+      watch(['modules/angular2/**'], { ignoreInitial: true }, [
         '!build/tree.dart',
         '!test.unit.dart/karma-run'
       ]);