This reverts commit 609aaa55.

Reason for revert:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/22157

Original change's description:
> [bigint] Serialization support for BigInts
> 
> Bug: v8:6791
> Change-Id: I6d428d0bfc08b7447cd4a961b9f4053c89ed158b
> Reviewed-on: https://chromium-review.googlesource.com/952626
> Reviewed-by: Adam Klein <adamk@chromium.org>
> Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51795}

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

Change-Id: I3c5ab51c40fcd897638d039d433cd764ca7f4e77
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6791
Reviewed-on: https://chromium-review.googlesource.com/954942Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51796}