This removes the "AboutToRun" callback. It makes not much
sense as it is not actually called before a test is run,
but just before the results are retrieved from the results
queue. Therefore, from an information-value p-o-v it is
redundant to the "HasRun" callback.

This also reduces log size on the bots by 50%, in order to
reduce buildbot slowness, which is tied to the amount
of logs.

Review URL: https://codereview.chromium.org/1874973003

Cr-Commit-Position: refs/heads/master@{#35382}