This reverts commit 4a45f35f.

Reason for revert: https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20-%20debug%20builder/builds/25471 

Original change's description:
> [wasm] Consolidate function table representation.
> 
> This CL avoids the need to reference the function tables (and signatures)
> as either fixed arrays or vectors, preferring vectors.
> 
> The only place we need fixed arrays is on the compiled module, to support
> serialization. When we move off the GC heap, we'll also move away
> from fixed arrays in that last case.
> 
> The CL aids with getting wasm of the GC heap, by reducing the places 
> and representations we'll need to change  when changing the way we 
> reference fixed tables.
> 
> Bug: 
> Change-Id: Id4e43905a3df39062bf2839fa72dd5d9a0fe87da
> Reviewed-on: https://chromium-review.googlesource.com/588334
> Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
> Reviewed-by: Brad Nelson <bradnelson@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46917}

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

Change-Id: Ie7d04f7ec74d6d0b3783df1c78c91c100ab784f4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/588627Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46918}