Remove TaskScheduler::CreateAndSetDefaultTaskScheduler().

This method has been replaced by Create() and Start().

R=gab@chromium.org
TBR=gab@chromium.org
BUG=690706

Review-Url: https://codereview.chromium.org/2845913004
Cr-Commit-Position: refs/heads/master@{#467990}
7 files changed