[analyzer_cli] Remove unused dart:async imports

Change-Id: I58d1ca58e6d630aee928c6a7cb7fc97822a3be22
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/161449
Auto-Submit: Mike Fairhurst <mfairhurst@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

Author: MichaelRFairhurst

pkg/analyzer_cli/lib/src/analyzer_impl.dart

@@ -2,7 +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.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/dart/analysis/results.dart';

pkg/analyzer_cli/lib/src/batch_mode.dart

@@ -2,7 +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.
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:io' show exitCode, stdin;
 

pkg/analyzer_cli/lib/src/build_mode.dart

@@ -2,7 +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.
 
-import 'dart:async';
 import 'dart:io' as io;
 import 'dart:isolate';
 

pkg/analyzer_cli/lib/src/driver.dart

@@ -2,7 +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.
 
-import 'dart:async';
 import 'dart:io' as io;
 import 'dart:isolate';
 

pkg/analyzer_cli/lib/starter.dart

@@ -2,7 +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.
 
-import 'dart:async';
 import 'dart:isolate';
 
 import 'package:analyzer_cli/src/driver.dart';

pkg/analyzer_cli/test/analysis_options_test.dart

@@ -2,7 +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.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer_cli/src/driver.dart' show Driver, outSink, errorSink;

pkg/analyzer_cli/test/build_mode_test.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.
 
-import 'dart:async';
-
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer_cli/src/build_mode.dart';
 import 'package:analyzer_cli/src/driver.dart';

pkg/analyzer_cli/test/driver_test.dart

@@ -2,7 +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.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/error/error.dart';

pkg/analyzer_cli/test/package_prefix_test.dart

@@ -2,7 +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.
 
-import 'dart:async';
 import 'dart:io' show exitCode;
 
 import 'package:analyzer_cli/src/driver.dart' show Driver, outSink, errorSink;

pkg/analyzer_cli/test/utils.dart

@@ -2,7 +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.
 
-import 'dart:async';
 import 'dart:io';
 import 'dart:mirrors';