[dart2js] migrate main_call_stub_generator

Change-Id: I7f8933d9a1de71418f03cf48b4afebfbadc0d0bb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/267767
Reviewed-by: Stephen Adams <sra@google.com>
Reviewed-by: Nate Biggs <natebiggs@google.com>
Commit-Queue: Sigmund Cherem <sigmund@google.com>

Author: sigmundch

pkg/compiler/lib/src/js_emitter/main_call_stub_generator.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.10
-
 library dart2js.js_emitter.main_call_stub_generator;
 
 import 'package:compiler/src/options.dart';