[code] Remove "machine resources" when deleting a workspace

[akosyakov]

A user can see a list of all synchronised machines (workspaces) in Code which grows infinitely with each new workspace. We should make sure that a machine gets removed as soon as an associated workspace is deleted.

[akosyakov]

We should figure out how to associated a machine with the workspace, right now the view is not very helpful. We also don't need to persist old revisions for this resource, a user never sees them and cannot rollback.