This reverts commit 5e76ff5a.

Reason for revert: tsan failures - https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20TSAN/builds/17574

Original change's description:
> Reland "[wasm] always allocate memory when guard regions are needed"
> 
> This reverts commit 7cf29d8d.
> 
> Original change's description:
> > [wasm] always allocate memory when guard regions are needed
> >
> > When using trap handlers, memory references do not get any checks inserted. This
> > means there is no check for a null memory as happens when the memory size is
> > 0. Normally this would be correctly caught as an out of bounds access, since the
> > low memory addresses are not normally mapped. However, if they were mapped for
> > some reason, we would not catch the out of bounds access.
> >
> > The fix is to ensure WebAssembly instances always have a guard region even if
> > the memory is size 0.
> >
> > Bug: chromium:769637
> 
> Change-Id: I09fdaea92b7ccb3a6cc9e28392171ec098538a00
> Reviewed-on: https://chromium-review.googlesource.com/695812
> Commit-Queue: Eric Holk <eholk@chromium.org>
> Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48293}

TBR=gdeepti@chromium.org,mtrofin@chromium.org,mlippautz@chromium.org,eholk@chromium.org,eholk@google.com,clemensh@chromium.org

Change-Id: I52d5354126158a92602b08c48703d562ac95075b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/699599Reviewed-by: Eric Holk <eholk@chromium.org>
Commit-Queue: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48294}