Revert of [proxies] Implement [[Enumerate]] and [[OwnPropertyKeys]] (patchset #3 id:40001 of https://codereview.chromium.org/1474083003/ )

Reason for revert:
[Sheriff] Speculative revert for gc mole:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20gcmole/builds/5164

Original issue's description:
> [proxies] Implement [[Enumerate]] and [[OwnPropertyKeys]]
>
> Both are integrated into JSReceiver::GetKeys().
>
> For now, the implementation ignores Symbol/DONT_ENUM filtering.
>
> BUG=v8:1543
> LOG=n
>
> Committed: https://crrev.com/42c6056e6f247724d14dc887f6619a6bf5867a97
> Cr-Commit-Position: refs/heads/master@{#32384}

TBR=verwaest@chromium.org,bmeurer@chromium.org,jkummerow@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:1543

Review URL: https://codereview.chromium.org/1482113002

Cr-Commit-Position: refs/heads/master@{#32385}