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The packages contains `__legacy__` folders which holds outdated or deprecated implementation.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.