Remove dummy ci.yml workflow

[GuySartorelli]

This repo has a dummy ci.yml workflow. This has been required until now for the merge-ups workflow to pass. As of https://github.com/silverstripe/gha-trigger-ci/pull/5 a repo doesn't need a dummy CI file for the mergeups workflow to pass.

Acceptance Criteria

• Remove ci.yml workflow file
• Add a hardcoded exception in https://github.com/silverstripe/module-standardiser so that a new ci.yml file isn't created for this repository next time that's run
• Create a card for CMS 6 to update the folder structure to the standard client/src so we can add a standard ci.yml for it.