Migrate physics tests to NNBD (#64584)

packages/flutter/test/physics/clamped_simulation_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/physics.dart';
 import 'package:flutter_test/flutter_test.dart';
 

packages/flutter/test/physics/friction_simulation_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/physics.dart';
 import 'package:flutter_test/flutter_test.dart';
 

packages/flutter/test/physics/gravity_simulation_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/physics.dart';
 import 'package:flutter_test/flutter_test.dart';
 

packages/flutter/test/physics/near_equal_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/physics.dart';
 
 import '../flutter_test_alternative.dart';

packages/flutter/test/physics/newton_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/physics.dart';
 import 'package:flutter/widgets.dart';
 

packages/flutter/test/physics/tolerance_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/physics.dart';
 import 'package:flutter_test/flutter_test.dart';
 

packages/flutter/test/physics/utils_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/physics.dart';
 import 'package:flutter_test/flutter_test.dart';