"ExpressionProductions" was missing the plural. I don't think this
changed any behavior, but I'd rather be safe than sorry. Also
removed redundant mention of TailCall production.

A future patch will attempt to make calls to Accumulate make more sense,
in general.

R=littledan@chromium.org

Review-Url: https://codereview.chromium.org/2270153002
Cr-Commit-Position: refs/heads/master@{#38842}