This removes a duplicate control scope. The visitor for ForOfStatement
nodes in the AST uses VisitIterationBody which pushes a separate control
scope. The number of control scopes will be off when we use them for
tracking loop depths.

R=rmcilroy@chromium.org

Review-Url: https://codereview.chromium.org/2164503005
Cr-Commit-Position: refs/heads/master@{#37930}