This was the last one marked as a zombie. There might be others I don't
know about, but except for in the hypothetical case of a thread dying
due to an async exception before it can wait on a process it started, I
don't know of any.
It would probably be safe to remove the reapZombies now, but let's wait
and so that in its own commit in case it turns out to cause problems.
This commit was sponsored by Boyd Stephen Smith Jr. on Patreon.
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