This reverts commit 163c1c82.

Reason for revert: Throws std::bad_alloc on linux: https://build.chromium.org/p/client.v8/builders/V8%20Linux/builds/21927; needs investigation.

Original change's description:
> [wasm] Gracefully handle malformed custom sections in WebAssembly.Module.customSections().
> 
> R=​clemensh@chromium.org
> BUG=chromium:789952
> 
> Change-Id: Ida627fa6cdeacff01a0ec4d20e58281f17528010
> Reviewed-on: https://chromium-review.googlesource.com/800941
> Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
> Commit-Queue: Ben Titzer <titzer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49767}

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

Change-Id: I63fbd8f55025f53c453e91d0f7a181c21ae53a39
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:789952
Reviewed-on: https://chromium-review.googlesource.com/801554Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49768}