This enables the {BytecodeGraphBuilder} whenever heuristics in the
compilation pipeline determine both Ignition and TurboFan to be used.
There no longer needs to be an explicit flag passed in order to build
graphs from bytecode.

R=bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2363413005
Cr-Commit-Position: refs/heads/master@{#40045}