[dap] Remove some code that's not longer required (#98928)

packages/flutter_tools/lib/src/debug_adapters/flutter_adapter.dart

@@ -5,7 +5,7 @@
 import 'dart:async';
 import 'dart:math' as math;
 
-import 'package:dds/dap.dart' hide PidTracker, PackageConfigUtils;
+import 'package:dds/dap.dart' hide PidTracker;
 import 'package:meta/meta.dart';
 import 'package:vm_service/vm_service.dart' as vm;
 
@@ -19,7 +19,7 @@ import 'mixins.dart';
 
 /// A DAP Debug Adapter for running and debugging Flutter applications.
 class FlutterDebugAdapter extends DartDebugAdapter<FlutterLaunchRequestArguments, FlutterAttachRequestArguments>
-    with PidTracker, PackageConfigUtils {
+    with PidTracker {
   FlutterDebugAdapter(
     ByteStreamServerChannel channel, {
     required this.fileSystem,
@@ -36,7 +36,6 @@ class FlutterDebugAdapter extends DartDebugAdapter<FlutterLaunchRequestArguments
           logger: logger,
         );
 
-  @override
   FileSystem fileSystem;
   Platform platform;
   Process? _process;

packages/flutter_tools/lib/src/debug_adapters/flutter_test_adapter.dart

@@ -5,7 +5,7 @@
 import 'dart:async';
 import 'dart:math' as math;
 
-import 'package:dds/dap.dart' hide PidTracker, PackageConfigUtils;
+import 'package:dds/dap.dart' hide PidTracker;
 import 'package:meta/meta.dart';
 import 'package:vm_service/vm_service.dart' as vm;
 
@@ -19,7 +19,7 @@ import 'mixins.dart';
 
 /// A DAP Debug Adapter for running and debugging Flutter tests.
 class FlutterTestDebugAdapter extends DartDebugAdapter<FlutterLaunchRequestArguments, FlutterAttachRequestArguments>
-    with PidTracker, PackageConfigUtils, TestAdapter {
+    with PidTracker, TestAdapter {
   FlutterTestDebugAdapter(
     ByteStreamServerChannel channel, {
     required this.fileSystem,
@@ -36,7 +36,6 @@ class FlutterTestDebugAdapter extends DartDebugAdapter<FlutterLaunchRequestArgum
           logger: logger,
         );
 
-  @override
   FileSystem fileSystem;
   Platform platform;
   Process? _process;

packages/flutter_tools/lib/src/debug_adapters/mixins.dart

@@ -2,48 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import '../base/file_system.dart';
 import '../base/io.dart';
 
-/// A mixin providing some utility functions for locating/working with
-/// package_config.json files.
-///
-/// Adapted from package:dds/src/dap/adapters/mixins.dart to use Flutter's
-/// dart:io wrappers.
-mixin PackageConfigUtils {
-  abstract FileSystem fileSystem;
-
-  /// Find the `package_config.json` file for the program being launched.
-  File? findPackageConfigFile(String possibleRoot) {
-    // TODO(dantup): Remove this once
-    //   https://github.com/dart-lang/sdk/issues/45530 is done as it will not be
-    //   necessary.
-    File? packageConfig;
-    while (true) {
-      packageConfig = fileSystem.file(
-        fileSystem.path.join(possibleRoot, '.dart_tool', 'package_config.json'),
-      );
-
-      // If this packageconfig exists, use it.
-      if (packageConfig.existsSync()) {
-        break;
-      }
-
-      final String parent = fileSystem.path.dirname(possibleRoot);
-
-      // If we can't go up anymore, the search failed.
-      if (parent == possibleRoot) {
-        packageConfig = null;
-        break;
-      }
-
-      possibleRoot = parent;
-    }
-
-    return packageConfig;
-  }
-}
-
 /// A mixin for tracking additional PIDs that can be shut down at the end of a debug session.
 ///
 /// Adapted from package:dds/src/dap/adapters/mixins.dart to use Flutter's