This reverts commit 3913bde1.

Reason for revert: Reason for revert fixed.

Original change's description:
> Revert "[wasm] Rename TestingModule to TestingModuleBuilder."
> 
> 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/622567
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#47448}

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

Change-Id: Idce6f1ca8ed0ea80edb50292e9b6e2d7712f29cf
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/622034Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47454}