job.py: Do not call Process.close()
As we handle subprocess termination by pid with an asyncio child watcher, the multiprocessing.Process object does not get notified when the process terminates. And as the child watcher reaps the process, the pid is no longer valid and the Process object is unable to check whether the process is dead. This results in Process.close() raising a ValueError.
This is a partial revert of 9c23ce5c
Fixes: #1243 (closed)