Remove `__legacy__` folders from packages & refactor the usage

### Current Limitation

The packages contains `__legacy__` folders which holds outdated or deprecated implementation. Keeping legacy code can lead to confusion and maintenance issues.

### Suggested Improvement

Remove the entire `__legacy__` folder from the packages and refactor any code that references or depends on its contents.

### Please select the package issue is related to

@asgardeo/browser, @asgardeo/express, @asgardeo/javascript, @asgardeo/node

### Version

N/A

### Reporter Checklist

- [x] I have searched the existing issues and this is not a duplicate.
- [x] I have provided all the necessary information.
- [x] I have verified the improvement is not available in the latest version of the package.

まず、@asgardeo/browser、@asgardeo/express、@asgardeo/javascript、@asgardeo/node パッケージで、__legacy__ ディレクトリとその内容への参照を検索します。フォルダーを削除して呼び出し元をリファクタリングする前に、各依存関係を追跡してください。影響を受けるパッケージを壊すことなく、legacy フォルダーとその参照がなくなれば完了です。

索引モデルが issue の本文から書いたものです。