Fixed flaky test `RemoveExecutorUponFailedLaunch`.
Fixed flaky test `RemoveExecutorUponFailedLaunch`.

The scheduler `statusUpdate` call expectation is not
necessary and may not be satisfied in some cases, leading
to flakiness. Replaced `WillOnce` with `AtMost(1)`.

Review: https://reviews.apache.org/r/68803/

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