This reverts commit e110b59c.

Reason for revert: Breaks arm debug on chromebook hardware:
https://build.chromium.org/p/client.v8.ports/builders/V8%20Arm%20-%20debug/builds/5335

Original change's description:
> [bigint] Fix early-return in asIntN
> 
> For "top digit" (of the result) comparison to be applicable, we must
> also check that there are no further digits in the source.
> 
> Bug: v8:7150
> Change-Id: I6ad317f6f600e11fef59b9907da1055e5586a3a8
> Reviewed-on: https://chromium-review.googlesource.com/804639
> Reviewed-by: Georg Neis <neis@chromium.org>
> Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49846}

TBR=jkummerow@chromium.org,neis@chromium.org

Change-Id: I5dae82696d3ecb9602f73a2ff4760ed7bbcef1c5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7150
Reviewed-on: https://chromium-review.googlesource.com/806838Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49847}