kokoro: Fix MSL validation

PATH was overwritten immediately after adding the metal shader compiler.

Fixed: tint:1700
Change-Id: Iab5b74dbed9a20aa068678839fbc2ff1fa268d9a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/116299
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
diff --git a/infra/kokoro/windows/build.bat b/infra/kokoro/windows/build.bat
index eac0a71..baa29c7 100644
--- a/infra/kokoro/windows/build.bat
+++ b/infra/kokoro/windows/build.bat
@@ -151,8 +151,6 @@
 rem Run tests with DXC, FXC and Metal validation
 set OLD_PATH=%PATH%
 set PATH=C:\Program Files\Metal Developer Tools\macos\bin;%PATH%
-where metal.exe
-set PATH=%DXC_PATH%;%D3DCOMPILER_PATH%;%OLD_PATH%
 call git bash -- ./test/tint/test-all.sh ../dawn-build/tint.exe --verbose || goto :error
 set PATH=%OLD_PATH%
 @echo off