Fix race condition in test/del.js
Fix race condition in test/del.js

Problem: The test wasn't actually waiting for all messages to be
deleted before it checked to ensure that they were all deleted. I'm not
sure why the recent queue change would make this bug visible, but it
**is** a bug in the test.

Solution: Wait until all messages have been deleted until trying to
confirm that they've all been deleted.

ssbc/secure-scuttlebutt