Remove useless t.done() in worker promise tests

Promise tests complete when their promise settles. Calling t.done() is
not required.

Bug: 330885075
Change-Id: I496b2222a47983536053218075b03b829b191e3c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5392061


Commit-Queue: Jean-Philippe Gravel <jpgravel@chromium.org>
Reviewed-by: Andres Ricardo Perez <andresrperez@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282154}