chore(demo-site): remove workflow

[andy-blum]

This PR removes the publish-demo-site workflow as it is no longer needed. The demo-site package has been removed from this project, and https://carbon-design-system.github.io/devtools/ is published from the gh-pages branch of this repo.

Changelog

Removed

• Removed github workflow for publishing the demo site from the base branch.

Testing / Reviewing

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[motou]

Unfortunately, I overlooked the workflow to build the gh-page. It is used to generate the codes for the gh-page branch and that is why it is called "deploy-gh-page". See https://github.com/carbon-design-system/devtools/actions/runs/9210743497/job/25338451733#step:5:30