This reverts commit 0aac3884.

Reason for revert: Various performance regressions (Blink and JSTests).

Original change's description:
> [turbofan] Be more consistent about Smi comparisons.
> 
> This changes SimplifiedLowering to be more consistent when chosing Smi
> representation as input for Number comparisons. We already had some
> isolated logic for doing (speculative) Number comparisons on Smis, but
> only in the case where that decision was based on type feedback, not on
> information already present in the graph.
> 
> Bug: v8:7703
> Change-Id: I25370ade630917675a6ac79b5ae6a8afd253dfc7
> Reviewed-on: https://chromium-review.googlesource.com/1196422
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#55518}

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

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:7703, chromium:881758, chromium:881759, chromium:881760
Change-Id: I4af9c0b0ad37dea17ceabeb721c92a7cc978987a
Reviewed-on: https://chromium-review.googlesource.com/1213185Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55720}