Revert of PPC: Resolve references to "this" the same way as normal variables (patchset #1 id:1 of https://codereview.chromium.org/1129803003/)

Reason for revert:
Original commit was reverted.

Original issue's description:
> PPC: Resolve references to "this" the same way as normal variables
>
> Port 18619d35
>
> Original commit message:
> 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>.
>
> R=wingo@igalia.com, dstence@us.ibm.com,  michael_dawson@ca.ibm.com
> BUG=
>
> Committed: https://crrev.com/e0ec097b2f49c4c99a2e9490f4b1a09e02abfd4d
> Cr-Commit-Position: refs/heads/master@{#28272}

TBR=dstence@us.ibm.com,michael_dawson@ca.ibm.com,wingo@igalia.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1132513005

Cr-Commit-Position: refs/heads/master@{#28305}