This reverts commit c3bd741e.

Reason for revert: Breaks layout tests:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/20384

Original change's description:
> Fix "this" value in lazily-parsed module functions.
> 
> When preparsing top-level functions in a module, we didn't track
> unresolved variables. Consequently, "this" ended up referencing
> the global "this", which has the wrong value (in a module "this"
> is supposed to be the undefined value).
> 
> This patch fixes that. This also lets us stop forcing context
> allocation of all variables in module scopes, which the patch
> takes care of as well.
> 
> Bug: chromium:791334
> Change-Id: Ifac1f1adc033f3facfb3d29dd4bca32ee27bffcf
> Reviewed-on: https://chromium-review.googlesource.com/808938
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Reviewed-by: Adam Klein <adamk@chromium.org>
> Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
> Commit-Queue: Georg Neis <neis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50025}

TBR=adamk@chromium.org,marja@chromium.org,neis@chromium.org,kozyatinskiy@chromium.org

Change-Id: I81f69334ed2ce104c00e6205d50001e4bdf07d15
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:791334
Reviewed-on: https://chromium-review.googlesource.com/822258Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50036}