Remove leftover use of proxy Dawn GN group targets.

Bug: chromium:1064305
Change-Id: Id49edb06b68f2ce91fc6edc5f092a2b2dcb165f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2143795Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757866}

gpu/command_buffer/common/BUILD.gn

@@ -181,7 +181,7 @@ source_set("webgpu_sources") {
 
   public_deps = [
     ":common",
-    "//third_party/dawn/src/dawn_wire:libdawn_wire_headers",
+    "//third_party/dawn/src/dawn_wire:dawn_wire_headers",
     "//ui/gl:buildflags",
   ]
 }