Remove pack-objects limit by user_id and repository
$(!4555 (merged))+ taught the pack objects hook RPC to limit concurrent pack objects processes by either repository or user. But, through discussions on #4401 (comment 1084920115) as well as other discussions with team members, the consensus seems to be that the better way to limit is by repository.
We should remove the code in internal/gitaly/service/hook/pack_objects.go
that allows limiting by user, and modify the config now that we know that we want to use repository as the limiting key.