slapos_pdm: Drop needless cleanup on Software Release

The state of Software Release being cleaned up or not is really never
known, so simply drop the concept.

Use case to cover, is some developer having upgrade_scope=auto set and
installing archived SRs - it IS expected that such SR would be cleaned
if not used.
5 jobs for fix/computer-archived-sr-cleanup in 0 seconds (queued for 1 second)
Status Job ID Name Coverage
  External
failed SlapOS-Master.UnitTest-Luke

running SlapOS-Master.UnitTest-Luke

24006:22:35

failed SlapOS-Master.UnitTest-Luke

23:33:04

failed SlapOS-Master.UnitTest-Luke

31:45:03

failed SlapOS-Master.UnitTest-Luke

11:26:23