Job.job_id is populated before job creation in bigquery-usage

[dhermes]

The job_id property uses the _properties returned from the server. It seems the original intent was a uuid.uuid4() on instance creation.

[tseaver]

#1469 removes the job_id property altogether: it is redundant to the user-supplied name.

[dhermes]

👍 That PR removes it from the docs, but not from the object, is that correct?

[tseaver]

I meant to remove it from the object as well. (looks) Nope, missed that it was being covered indirectly via the client.