refactor: Remove recent sprite changes from external_tileset

[thedyze]

Checklist

Required

• [x] I wrote the PR title in conventional commit format.
• [x] I ran the code formatter.
• [x] I linked any relevant issues using github keyword syntax so it can be closed automatically.
• [x] I have committed my changes to new branch that isn't main so it won't cause conflict when updating main branch later.

Optional

Purpose of change

To cleanup after adding recent sprite changes as a mainline mod.

Describe the solution

Remove recent sprite changes from external_tileset as they now exist as a mod https://github.com/cataclysmbnteam/Cataclysm-BN/pull/5702

Describe alternatives you've considered

Testing

Additional context

Also removed changes added to tileset documentation