Revert of Encode reservation meta data in the snapshot blob. (patchset #3 id:40001 of https://codereview.chromium.org/781443002/)

Reason for revert:
[sheriff] Breaks http://build.chromium.org/p/client.v8/builders/V8-Blink%20Linux%2064/builds/1540

Original issue's description:
> Encode reservation meta data in the snapshot blob.
>
> This also makes reserving multiple chunks per object space possible.
>
> R=vogelheim@chromium.org

TBR=vogelheim@chromium.org,baixo@chromium.org,yangguo@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/780833002

Cr-Commit-Position: refs/heads/master@{#25654}