Related to #46453
The test was flaky because Submit() returns a Future and executes
asynchronously. The test was setting sig=true immediately after Submit()
returned, but the task's Run() might not have completed yet, causing
mock expectation failures.
Fix by calling future.Await() to wait for task execution to complete
before signaling. Also remove dead commented code.
Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>