Remove auto-deploy legacy job

What does this MR do?

After gitlab-com/gl-infra/delivery#1578 (closed), we trigger individual deployer pipelines for each one of our environments. auto_deploy:deploy is a legacy job that triggers an individual deployer pipeline for all our environments, currently it's a no-op.

Since we're moving forward with individual deployments, we can remove this legacy job now.

Related to gitlab-com/gl-infra/delivery#1689 (closed)