Allow delete() to work on decommissioned systems

[araglu]

The @_ensure_connected decorator forces a connection attempt to the HPC before deleting the job, and that fails on any system that no longer exists.

[sdc50]

By removing @_ensure_connected are we just hoping that the client is already connected by the time this is called? I wonder if we can isolate where it is called.

[araglu]

That decorator is used on other functions like self.stop() and self.client.call() which are called after the logic to avoid working on decommissioned systems. That's why self.clean() doesn't have that decorator and why delete() should not have it.

I just thought about having @_ensure_connected check for decommissioned systems, but I still want delete() to clean up local directories.