Revert of Resolve references to "this" the same way as normal variables (patchset #11 id:240001 of https://codereview.chromium.org/1097283003/)

Reason for revert:
nosnap failures

Original issue's description:
> Resolve references to "this" the same way as normal variables
>
> Make the parser handle references to "this" as unresolved variables, so the
> same logic as for the rest of function parameters is used for the receiver.
> Minor additions to the code generation handle copying the receiver to the
> context, along with the rest of the function parameters.
>
> Based on work by Adrian Perez de Castro <aperez@igalia.com>.
>
> BUG=
> LOG=N
>
> Committed: https://crrev.com/18619d355192e2699203d12d9ebb9caea107b693
> Cr-Commit-Position: refs/heads/master@{#28236}

TBR=rossberg@chromium.org,mstarzinger@chromium.org,dslomov@chromium.org,adamk@chromium.org,arv@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1113133006

Cr-Commit-Position: refs/heads/master@{#28238}