Revert of [compiler] Prepare for partially shipping Ignition. (patchset #1 id:1 of https://codereview.chromium.org/2443573002/ )

Reason for revert:
Causes regressions: https://bugs.chromium.org/p/chromium/issues/detail?id=658711

Original issue's description:
> [compiler] Prepare for partially shipping Ignition.
>
> This prepares the code-base so that Ignition can be enabled on a certain
> subset of compilations without setting the {FLAG_ignition} flag (which
> enables Ignition on all compilations). We should not check the flag in
> question explicitly anywhere outside of the compiler heuristics.
>
> R=mvstanton@chromium.org

BUG=chromium:658711
TBR=mvstanton@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.

Review-Url: https://codereview.chromium.org/2448443002
Cr-Commit-Position: refs/heads/master@{#40534}