Only send DOWNLOAD_COMPLETE broadcast once.
Jeff Sharkey authored
Apps might end up confused if we tell them a download was completed
multiple times, so only send the broadcast exactly once when we
transition it into a "completed" state, either during an update() or
a delete() operation.

Test: verified single broadcast with test app
Bug: 31619480
Change-Id: I0b9139ea0e37f6d212b84314048692cd0c4f9cdf
f96f51e8