CI: remove `branch_release_job`

Adding a manual step to MR pipelines makes them appear as Blocked rather than Green, which confused some contractors.

The role of branch_release_job is to upload sast-rules.zip to the project's generic package registry to enable manual inspection. However it already possible to download sast-rules.zip manually as it is an artifact of the build-and-verify job.

Therefore, I believe we can remove the branch_release_job job added by !316 (merged), so that MRs are shown as Green again, without losing the ability to manually investigate the produced artifacts.