This reverts commit 6da438fd.

Reason for revert:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20nosnap%20-%20debug/builds/18287

Original change's description:
> [runtime] introduced instrance type for each context type
> 
> Each context type get own instance type:
> - we can make CSA checks more strict in couple places,
> - it is requires step for advanced evaluation without side effects.
> 
> R=​yangguo@chromium.org
> 
> Bug: v8:7588
> Change-Id: I585e8b55a280a909fc3c6069ed30e34b7040d0c7
> Reviewed-on: https://chromium-review.googlesource.com/977041
> Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52191}

TBR=yangguo@chromium.org,mstarzinger@chromium.org,kozyatinskiy@chromium.org

Change-Id: I17a24b5b99552941d7a8ec54ebf6d11d6d1a66d8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7588
Reviewed-on: https://chromium-review.googlesource.com/977974Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52193}