React Intro: Remove additional resources

[Desel72]

Because

This PR addresses GitHub issue #30916 which requests the removal of Additional resources sections from React Introduction lessons. The changes streamline the curriculum by removing supplemental content to focus students on core lesson material.

This PR

• Removed the entire "Additional resources" section from Introduction to React lesson
• Removed the entire "Additional resources" section from Setting Up a React Environment lesson
• Removed the entire "Additional resources" section from React Components lesson

Issue

Closes #30916

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide

[mao-sz]

Thanks. You've left an extra blank line at the end of each of these lessons, so these must be removed to pass the linter checks before I can merge.

Info on running the linter locally

[Desel72]

@mao-sz Could you please review again? thank you

[mao-sz]

Thanks for fixing that. A heads up that you can request a re-review via the re-review button in the top-right (see image below)