Remove docs-build.yml and docs-cleanup.yml workflows

[Copilot]

Removes the docs-build.yml and docs-cleanup.yml GitHub Actions workflow files since this repository is not publishing docs to the public docs site.

[mergify]

This pull request does not have a backport label. Could you fix it @Copilot? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• v7.x is the label to automatically backport to the 7.x branch.
• v7./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[github-actions]

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[natasha-moore-elastic]

hey @Mpdreamz, just checking we'll still be able to publish docs to elastic.co/guide from this repo when these workflows are removed?

[Mpdreamz]

yep! these workflows are only for /docs but security-docs on main doesn't participate there :) see: https://github.com/elastic/docs-builder/blob/main/config/assembler.yml