Remove the exported build of the WebGPU CTS from WPT

Updates the README in WPT to reflect this, and Chromium's roll script so
that it doesn't roll into WPT.

And, unrelatedly, removes JusSn from the suggested_reviewers as he is
no longer actively working on WebGPU.

Rationale:

These tests test an unstable, constantly changing API. Because of this,
it's not practical for browser implementations to try to sync on a
single version of the test suite which is auto-imported/exported from
WPT. Auto-imports in any browser will necessarily result in test
failures just because the tests have changed to match some API change.

Instead, for the moment, browsers should pin ("vendor") a particular
version of the WebGPU CTS, and may include a built version of it in
their equivalent of "wpt_internal" for automated testing.

Discussion: web-platform-tests#24699

Bug: None
Change-Id: Iaabd81ef646404ab7f6e8cc19a884b15f5306bca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2353550
Reviewed-by: Rakib Hasan <[email protected]>
Reviewed-by: Austin Eng <[email protected]>
Commit-Queue: Kai Ninomiya <[email protected]>
Cr-Commit-Position: refs/heads/master@{#797946}

webgpu/META.yml

@@ -1,5 +1,4 @@
 spec: https://gpuweb.github.io/gpuweb/
 suggested_reviewers:
   - kainino0x
-  - JusSn
   - kvark

webgpu/README.md

@@ -5,6 +5,13 @@ support and hardware support, so this API cannot run on most automated testing
 infrastructure. Tests inside this directory should always be skipped if
 appropriate GPU hardware is not available.
 
-The contents of this directory are automatically generated from TypeScript
+~~The contents of this directory are automatically generated from TypeScript
 sources which live upstream in the [WebGPU CTS](https://github.com/gpuweb/cts).
-They are periodically built and pushed to WPT.
+They are periodically built and pushed to WPT.~~
+
+**NOTE:** This directory is currently empty while WebGPU is in flux, as it's
+not practical for browser developers to sync their WebGPU implementations with
+WPT auto-import and auto-export of these tests. Instead, browsers should pin
+("vendor") a specific version of the gpuweb/cts repository, and check the built
+files into the browser repository as non-exported wpt tests (like Chromium's
+`wpt_internal`).