chore: remove legacy docbot and apibot scripts

[paulbalandan]

Description
Follow-up to #10382. This PR removes the remaining legacy documentation build scripts in admin/, which have been superseded by GitHub Actions:

• docbot built the User Guide with Sphinx and force-pushed it to the gh-pages branch of this repo. This is now done automatically by the "Deploy User Guide (latest)" workflow (deploy-userguide-latest.yml) on every push to develop that touches user_guide_src/.
• apibot built the API docs with phpDocumentor and force-pushed to codeigniter4/api. This is now done by the "Deploy API Documentation" workflow (deploy-apidocs.yml) on every push to develop that touches system/.
• alldocs only ran the two scripts above.

Besides being redundant, both scripts git push -f from a maintainer's machine to branches now owned by the workflows, so any manual run would fight with the automated deploys. docbot's secondary use (previewing user guide changes locally) is covered by plain make html.

Also removed: the docbot.md and apibot.md writeups, the docbot entry in admin/README.md, and the three allowlist entries in utils/check_permission_x.php.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide