Revert "Return report in Security Report Schemas 15.0.0"

Why is this change being made?

This MR reverts the change introduced with !2798 (merged). This change was unintentionally breaking for self-managed instances prior to %15.5, as they do not yet support schema version 15.0.0 but they are pulling all 5.x.x versions of GCS. We've decided to revert the change until we can figure out how to implement it in a way that is backwards-compatible for GitLab 15.0 - 15.4