Remove RESTRUCTURE.md since the work has been completed

[bvandermoon]

Description

Cleaning up the codebase by removing RESTRUCTURE.md. This work is finished and some time has already passed. The file is still referenced in Latest News for those who haven't seen it. All MaxText links to this file include a specific-commit, so the links will continue working.

Tests

N/A - removing a markdown file only

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[richjames0]

lgtm