Revert of Always deserialize scope infos for parsing (patchset #3 id:40001 of https://codereview.chromium.org/2280933002/ )

Reason for revert:
Significantly tanks parsing. We probably should just keep on doing what we're doing: partially deserialize while resolving variables. If we do scope-info backed resolution after regular resolution based on remaining free variables, we can probably reduce the time-frame of that part. We soon after anyway need to sync with the main thread.

Original issue's description:
> Always deserialize scope infos for parsing
>
> When looking up variables in the ScopeInfo, we did a linear scan of the
> ScopeInfo. Since that's unacceptably slow, a context slot cache was added
> that would speed up repeated lookups of the same variable.
>
> Instead, just always fully convert the ScopeInfo into scopes, so they can
> lookup variables without scanning the ScopeInfo.
>
> This also allows for removing the now unused ContextSlotCache.
>
> R=adamk@chromium.org,verwaest@chromium.org,marja@chromium.org
> BUG=v8:5315
>
> Committed: https://crrev.com/81f824cad18e4dc873a8838943217eb9c9f0c1f0
> Cr-Commit-Position: refs/heads/master@{#38953}

TBR=adamk@chromium.org,marja@chromium.org,jochen@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:5315

Review-Url: https://codereview.chromium.org/2287783003
Cr-Commit-Position: refs/heads/master@{#38958}