remove unsound mode web test (#118256)

dev/integration_tests/web/lib/null_assert_main.dart

@@ -1,24 +0,0 @@
-// Copyright 2014 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// ignore_for_file: enable_null_safety
-
-// @dart = 2.8
-
-import 'null_enabled_api.dart';
-
-void main() {
-  dynamic error;
-  try {
-    // Validate that a generated null assertion is thrown.
-    methodThatAcceptsNonNull(null);
-  } catch (err) {
-    error = err;
-  }
-  if (error is AssertionError) {
-    print('--- TEST SUCCEEDED ---');
-  } else {
-    print('--- TEST FAILED ---');
-  }
-}