States and Effects: Amend additional resources

[Desel72]

Because

This PR addresses GitHub issue #30917 which requests amendments to the States and Effects lessons. The changes streamline the curriculum by removing supplemental Additional resources sections and updating a broken/outdated link to a more reliable source.

This PR

• Replaced the React reconciliation link in Introduction to State assignment section from Medium article to GeeksforGeeks article
• Removed the entire "Additional resources" section from Introduction to State lesson
• Removed the entire "Additional resources" section from More on State lesson
• Removed the entire "Additional resources" section from How to Deal with Side Effects lesson

Issue

Closes #30917

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