Revert of [parsing] Fix maybe-assigned for loop variables. (patchset #3 id:40001 of https://codereview.chromium.org/2673403003/ )

Reason for revert:
Speculative revert because of https://codereview.chromium.org/2679163002/.

Original issue's description:
> [parsing] Fix maybe-assigned for loop variables.
>
> Due to hoisting, the value of a 'var'-declared variable may actually change even
> if the code contains only the "initial" assignment, namely when that assignment
> occurs inside a loop.  For example:
>
>   let i = 10;
>   do { var x = i } while (i--):
>
> As a simple and very conservative approximation of this, we explicitly mark
> as maybe-assigned any non-lexical variable whose "declaration" does not
> syntactically occur in the function scope.  (In the example above, it
> occurs in a block scope.)
>
> BUG=v8:5636
>
> Review-Url: https://codereview.chromium.org/2673403003
> Cr-Commit-Position: refs/heads/master@{#42989}
> Committed: https://chromium.googlesource.com/v8/v8/+/a33fcd663b28b8846e12b97c30d6e7d837767f86

TBR=marja@chromium.org,adamk@chromium.org,neis@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:5636

Review-Url: https://codereview.chromium.org/2679263002
Cr-Commit-Position: refs/heads/master@{#43010}