packaging: Stop autosubmitting built packages
For release builds, the current Jenkins pipeline always issues an OBS submit
request from the :snapshots repository where the just-built package is
uploaded to its final destination.
Unfortunately it doesn't check:
- whether the just-built version has been already uploaded to the same project, for instance when manually re-triggering the job
- whether the just-built version has been already uploaded to another project, for instance when doing a backport
Both occurrances lead to submit requests that, if accepted, cause OBS to export different sets of sources identified by the same (package,version) key, breaking the assumption about its uniqueness.
Debian tools would then become wildly confused, with reprepro not republishing the new sources since it already published sources with the same key.
Since the misplaced submit request are created too often (for instance when creating the jobs for a new branch, or even when updating them) and they can cause real, hard-to-detect damage, it's better to leave the submission fully manual until we move the affected packages to the GitLab-to-OBS workflow.