This reverts commit 972d460f.

Reason for revert: This CL is not the right solution, and it makes back-merging the right solution more difficult.

Original change's description:
> [wasm] Use 64-bit comparison for bounds checks on 64-bit platforms
> 
> By using 64-bit comparison we make sure that there will be no out of
> memory accesses even if there are stale values in the high word of a
> register.
> 
> R=​titzer@chromium.org
> 
> Change-Id: I2627b15e1598f35cc480d7028031e8de405164ea
> Reviewed-on: https://chromium-review.googlesource.com/721323
> Reviewed-by: Ben Titzer <titzer@chromium.org>
> Commit-Queue: Andreas Haas <ahaas@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48604}

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

Change-Id: I0c15e9d8ac72def2e22543a17366126d90a17918
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/721702Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48628}