There's no need to use a dedicated ChangeLoweringPhase before we go to
GenericLoweringPhase; instead that change lowering (which is really
simplified lowering by now) should run together with generic lowering.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1697133002

Cr-Commit-Position: refs/heads/master@{#34008}