[DevHub] Need to remove/update external resources links in the Shortcode Documentation page

Shortcode API documentation page contains links that do not exist.

documentation page link
https://developer.wordpress.org/apis/shortcode/#external-resources

Below is the screenshot for better understanding

Heads up @WordPress/docs-issues-coordinators, we have a new issue open. Time to use 'em labels.

Hi! I'd like to work on this issue. I'll check for updated resources or remove the broken links.

/assign

I checked the 4 flagged links:

"Add Shortcode – WordPress Code Snippet Generator" and "Shortcode summary by Aaron D. Campbell" still work and load correctly, so these can stay as-is.
"Innovative WordPress Shortcodes In Action" and "Simple shortcode-powered BBCode plugin" both link to plugins that have been closed by WordPress.org (Guideline Violation and Author Request, respectively), so these two should be removed.

I'll proceed to remove those two dead links from the External Resources section unless someone advises otherwise.