Removed unused method `packagesFile` from `ApplicationPackage`. (#95033)

The method name is confusing and the implementation in different
subclasses are pointing to different things.

packages/flutter_tools/lib/src/android/application_package.dart

@@ -203,9 +203,6 @@ class AndroidApk extends ApplicationPackage {
     );
   }
 
-  @override
-  File get packagesFile => file;
-
   @override
   String get name => file.basename;
 }

packages/flutter_tools/lib/src/application_package.dart

@@ -28,8 +28,6 @@ abstract class ApplicationPackage {
 
   String? get displayName => name;
 
-  File? get packagesFile => null;
-
   @override
   String toString() => displayName ?? id;
 }

packages/flutter_tools/lib/src/tester/flutter_tester.dart

@@ -36,9 +36,6 @@ class FlutterTesterApp extends ApplicationPackage {
 
   @override
   String get name => _directory.basename;
-
-  @override
-  File get packagesFile => _directory.childFile('.packages');
 }
 
 /// The device interface for running on the flutter_tester shell.

packages/flutter_tools/test/general.shard/tester/flutter_tester_test.dart

@@ -36,7 +36,6 @@ void main() {
     final FlutterTesterApp app = FlutterTesterApp.fromCurrentDirectory(fileSystem);
 
     expect(app.name, 'my_project');
-    expect(app.packagesFile.path, fileSystem.path.join(projectPath, '.packages'));
   });
 
   group('FlutterTesterDevices', () {