This reverts commit 517df524.

Reason for revert: Fails MSAN tests - https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/builds/20030

Original change's description:
> [parser] Implements proposal-numeric-separator.
> 
> https://github.com/tc39/proposal-numeric-separator
> 
> This proposal-numeric-separator extends NumericLiteral and
> allows developers to insert underscore(_) inside numeric literal.
> 
> Bug: v8:7317
> Change-Id: I2a1a45cd6fe09cc5df63433bc915988fde687a33
> Reviewed-on: https://chromium-review.googlesource.com/923441
> Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
> Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51671}

TBR=adamk@chromium.org,jkummerow@chromium.org,hablich@chromium.org,gsathya@chromium.org,mathias@chromium.org,goto@google.com,brn@b6n.ch

Change-Id: I6dcf46820caf20f28fbc11d94a5e8ced3cbbc78d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7317
Reviewed-on: https://chromium-review.googlesource.com/944767Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51672}