This reverts commit 1b35c0fa.

Reason for revert: Seems to reliably break a numerics test:
https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20-%20debug/31516

Original change's description:
> Improve NumberToString when cache miss and Smi
> 
> Cache miss was handled in runtime before. This change add fast path for
> Smi in this case.
> 
> Perf show 30% improvement for the following example.
> Before 67 ms
> After 42 ms
> 
> const start = new Date();
> const MAX = 1000000;
> for (var i = 0; i < MAX; i++) {
>     i.toString();
> }
> const end = new Date();
> console.log("Time :"+ (end-start));
> 
> Change-Id: I162e9c35f58551ca6a5a0efe79fb7c7b482a8594
> Bug: v8:10477
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2332866
> Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#69362}

TBR=jgruber@chromium.org,leszeks@chromium.org,duongn@microsoft.com

Change-Id: I80f6bdb0464c0034e6c4a16478848618cef7e046
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:10477
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2351389Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69365}