By now TurboFan is shipping on a broad range of language constructs and
wholesale disabling TurboFan can still be done with the --turbo-filter
flag. A dedicated flag controlling AST numbering heuristics is no longer
needed.

R=bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2155243006
Cr-Commit-Position: refs/heads/master@{#37900}