Revert "Add WebGPU to about:flags on Windows"

This reverts commit 953678c5.

Reason for revert: test failures: crbug.com/1017035

Original change's description:
> Add WebGPU to about:flags on Windows
> 
> Now that all of the work on the Chromium and Dawn side to support
> Windows has been complete, we need to add WebGPU to about:flags
> on Windows.
> 
> Bug: 966580
> Change-Id: I41d9f892be0d849c5ece1d5569f98344a7a92a1e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1873383
> Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
> Commit-Queue: Rafael Cintron <rafael.cintron@microsoft.com>
> Cr-Commit-Position: refs/heads/master@{#708405}

TBR=cwallez@chromium.org,sunnyps@chromium.org,rafael.cintron@microsoft.com

Change-Id: I3ee918a6073ea6244381ff497b078f424e179dfa
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 966580
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1875013Reviewed-by: Hajime Hoshi <hajimehoshi@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708497}

chrome/browser/about_flags.cc

@@ -4198,7 +4198,7 @@ const FeatureEntry kFeatureEntries[] = {
      FEATURE_VALUE_TYPE(
          autofill::features::kAutofillDoNotMigrateUnsupportedLocalCards)},
     {"enable-unsafe-webgpu", flag_descriptions::kUnsafeWebGPUName,
-     flag_descriptions::kUnsafeWebGPUDescription, kOsMac | kOsWin,
+     flag_descriptions::kUnsafeWebGPUDescription, kOsMac,
      SINGLE_VALUE_TYPE(switches::kEnableUnsafeWebGPU)},
 
 #if defined(OS_ANDROID)

ui/gl/features.gni

@@ -14,5 +14,5 @@ declare_args() {
   # Should Dawn support be compiled to back the WebGPU implementation.
   # Also controls linking Dawn depedencies in such as SPIRV-Tools and
   # SPIRV-Cross
-  use_dawn = is_mac || is_win
+  use_dawn = is_mac
 }