Revert "Dawn: use Dawn's temporary test targets for isolates."

This reverts commit 10edbbe8c9de9ae6942794d26c778d22ca3b5686.

Reason for revert: Causing purple on FYI bots:

<The executable does not exist or a dependent library is missing>
<Check for missing .so/.dll in the .isolate or GN file>
e.g., https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Release%20(Intel)/9078

Original change's description:
> Dawn: use Dawn's temporary test targets for isolates.
> 
> The plan is to move the actual test targets in Dawn to Dawn's
> src/test directory. This change makes Chrome temporarily point at
> some intermediate proxy targets, so we can move the real ones
> without breaking Chrome.
> 
> Bug: dawn:61
> Change-Id: I27a66a0daffe212da3fe2a0aaba7d4a250a376ea
> Reviewed-on: https://chromium-review.googlesource.com/c/1373892
> Reviewed-by: Corentin Wallez <cwallez@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Commit-Queue: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#615895}

TBR=thakis@chromium.org,senorblanco@chromium.org,cwallez@chromium.org

Change-Id: Ic5f3778259e37d3818e7dee1a04bb49a66bff27a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: dawn:61
Reviewed-on: https://chromium-review.googlesource.com/c/1374369
Reviewed-by: Stephen White <senorblanco@chromium.org>
Commit-Queue: Stephen White <senorblanco@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615942}
1 file changed