This reverts commit cc07ac73.

Reason for revert: Breaks benchmarks:
http://shortn/_POjH6zA7tp

Original change's description:
> [turbofan] Make sure TruncatingUseInfoFromRepresentation respects Smi representation.
> 
> Eventually, we want to fix this also for tagged pointers (tracking bug: https://crbug.com/v8/7162).
> 
> Bug: chromium:791245
> Change-Id: I93d6deff36cedcc9a4665fab0abe6fffdae9b61b
> Reviewed-on: https://chromium-review.googlesource.com/806457
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49850}

TBR=jarin@chromium.org,bmeurer@chromium.org

Change-Id: I0ff571b161ec40ba1f32ee048f8255c42414d8d2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:791245
Reviewed-on: https://chromium-review.googlesource.com/807985Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49853}