Revert of Add script context with context-allocated "const this" (patchset #7 id:120001 of https://codereview.chromium.org/1179893002/)

Reason for revert:
[Sheriff] Breaks gc mole:
http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20gcmole/builds/2435

Original issue's description:
> Add script context with context-allocated "const this"
>
> R=rossberg@chromium.org
> LOG=N
> BUG=498811
>
> Committed: https://crrev.com/fa32d461c16a053cc6d48d3fb326016bc2765765
> Cr-Commit-Position: refs/heads/master@{#28988}

TBR=rossberg@chromium.org,mstarzinger@chromium.org,wingo@igalia.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=498811

Review URL: https://codereview.chromium.org/1180043004

Cr-Commit-Position: refs/heads/master@{#28992}