Revert of Use a slot that is located on a heap page when removing invalid entries from the SlotsBuffer. (patchset #1 id:1 of https://codereview.chromium.org/1020853022/)

Reason for revert:
Reverting risky GC changes that block v8 roll.

Original issue's description:
> Use a slot that is located on a heap page when removing invalid entries from the SlotsBuffer.
>
> BUG=chromium:470801
> LOG=Y
>
> Committed: https://crrev.com/2f3a42f9a1d66ffc9d260d9700ff831c3aa1cd41
> Cr-Commit-Position: refs/heads/master@{#27467}

TBR=hpayer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:470801

Review URL: https://codereview.chromium.org/1033163002

Cr-Commit-Position: refs/heads/master@{#27490}