This reverts commit ed06fc91.

Reason for revert: Need to revert previous CL

Original change's description:
> [wasm] Rename TestingModule to TestingModuleBuilder.
> 
> This is a followup to moving the ModuleEnv to the compiler directory and
> making it immutable.
> 
> R=​mtrofin@chromium.org, ahaas@chromium.org
> 
> Bug: 
> Change-Id: I0f5ec1b697bdcfad0b4dc2bca577cc0f40de8dc0
> Reviewed-on: https://chromium-review.googlesource.com/616762
> Commit-Queue: Ben Titzer <titzer@chromium.org>
> Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
> Reviewed-by: Andreas Haas <ahaas@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#47419}

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

Change-Id: I9b3b379e89f523c2fcf205a1d268aa294bbc44ff
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/622567Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47448}