Revert of Provide a tagged allocation top pointer. (patchset #4 id:60001 of https://codereview.chromium.org/2028633002/ )

Reason for revert:
Seems to be causing flakiness in some wasm tests:

https://build.chromium.org/p/client.v8/builders/V8%20Linux/builds/10598
https://build.chromium.org/p/client.v8/builders/V8%20Win32%20-%20debug/builds/2528

Original issue's description:
> Provide a tagged allocation top pointer.
>
> Taking over http://crrev.com/1924223002.
>
> BUG=chromium:606711
> LOG=N
>
> Committed: https://crrev.com/f42c9e93c80fdf57e8f92bb87f6ed927d0ae4028
> Cr-Commit-Position: refs/heads/master@{#36633}

TBR=bmeurer@chromium.org,hpayer@chromium.org,machenbach@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:606711

Review-Url: https://codereview.chromium.org/2031493002
Cr-Commit-Position: refs/heads/master@{#36640}