Fix Error 500 when deleting a pipeline via the API

Merged Stan Hu requested to merge sh-fix-delete-pipeline-api into master

GitLab EE has an admin audit log that attempts to call full_path on the entity for metadata. Unlike a project or a group, a CI pipeline doesn't have this, so users deleting a pipeline would always hit an Error 500.

AuditEventService isn't equipped to handle logging of the destruction of entities such as CI pipelines. It's a project-level event that operates on a pipeline.

Rather than pollute the database with information that doesn't quite fit in the schema, let's remove it altogether.


CE backport:

Edited by Stan Hu