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.
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/55481
CE backport: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24291