Revert of Reapply "Resolve references to "this" the same way as normal variables"" (patchset #2 id:20001 of https://codereview.chromium.org/1136883006/)

Reason for revert:
Something is deserializing "this" declarations as Variable::NORMAL and not Variable::THIS https://codereview.chromium.org/1136123010/

Original issue's description:
> Reapply "Resolve references to "this" the same way as normal variables""
>
> This reapplies https://codereview.chromium.org/1136073002, along with
> the followups:
>
>   Remove Scope::scope_uses_this_ flag
>   https://codereview.chromium.org/1128963005
>
> and
>
>   PPC: Resolve references to "this" the same way as normal variables
>   https://codereview.chromium.org/1134073003
>
> R=yangguo@chromium.org, rossberg@chromium.org
> LOG=N
> BUG=
>
> Committed: https://crrev.com/1efc1e4f7a3d30d5225e9d5cb2585cad7cb17099
> Cr-Commit-Position: refs/heads/master@{#28458}

TBR=rossberg@chromium.org,yangguo@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1146733002

Cr-Commit-Position: refs/heads/master@{#28473}