This reverts commit c8e10a16.

Reason for revert: This CL causes problems with webpages in the wild: https://crbug.com/1056295

Original change's description:
> [wasm][liftoff] Implement Atomic(Compare)Exchange on x64
> 
> R=​clemensb@chromium.org
> 
> Bug: v8:10108
> Change-Id: Ic9ef9ba35218450d3f9e7838890c82b785c34da4
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2037433
> Commit-Queue: Andreas Haas <ahaas@chromium.org>
> Reviewed-by: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#66429}

TBR=ahaas@chromium.org,clemensb@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:10108
Change-Id: I69251b9e3de13d8314e413a4196c8185a73bfb5c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2078544Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66494}