chore(s2): update the original toaster component name on storybook

[kuflower]

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

🧢 Your Project:

[LFDanLu]

I suppose this was so the "Show code" block would show UNSTABLE_ToastContainer instead?

[snowystinger]

I suppose this was so the "Show code" block would show UNSTABLE_ToastContainer instead?

yep, confusing to people that they couldn't use it without the prefix