Form Validation lesson: Remove additional resources and replace one assignment

[carlosmperezm]

Because

It's part of the additional resources evaluation.

This PR

• Replace the current 3rd assignment with https://threadreaderapp.com/thread/1400388896136040454.html
• Remove the "Additional resources" section entirely

Issue

Closes #30739

Additional Information

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 for doing this. While we're at it, do you mind removing the blank lines between line items in the assignment? They're not actually necessary. At the same time, I'm not sure why the first assignment's "skip" bit is a child bullet... it can just be a new sentence as part of the main item, just like with the second bullet. If that can be changed too, that'd be awesome 👍

[carlosmperezm]

No worries, I've got you 👍