Remove unused al-folio Docker Hub publishing workflows

docker-slim.yml, deploy-docker-tag.yml, and deploy-image.yml only ever
push images to the theme author's own Docker Hub account and require
secrets (DOCKER_USERNAME/DOCKER_PASSWORD) this fork doesn't have.
docker-slim.yml's repository_owner guard was also written incorrectly
(mixing an expression with trailing text made it always-truthy), so it
kept running via workflow_run and failing at the login step.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: robbyahn