This flag is on by default for now. Whenever heuristics in the compiler
pipeline decide to use Ignition+TurboFan, then {BytecodeGraphBuilder} is
active. Removing the flag reduces maintenance overhead.

R=mvstanton@chromium.org

Review-Url: https://codereview.chromium.org/2437103002
Cr-Commit-Position: refs/heads/master@{#40639}