Don't update CMake for Windows Kokoro builds

The Radial Windows OS image for Kokoro comes with CMake 3.17.3, and we
only demand CMake 3.13 at the moment. The previous image had an older
version, so we had to update it before every build.

Bug: b/161221236
Change-Id: I5c3cdc3728c9c7ec5fb3fe43841d7f7cc3245abc
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/46528
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/tests/kokoro/gcp_windows/continuous.bat b/tests/kokoro/gcp_windows/continuous.bat
index 930dae8..3bd632c 100644
--- a/tests/kokoro/gcp_windows/continuous.bat
+++ b/tests/kokoro/gcp_windows/continuous.bat
@@ -12,8 +12,10 @@
 
 cd %SRC%\build || goto :error
 
-REM Update CMake
-choco upgrade cmake -y --limit-output --no-progress
+REM The currently used OS image comes with CMake 3.17.3. If a newer version is
+REM required one can update the image (go/radial/kokoro_windows_image), or
+REM uncomment the line below.
+REM choco upgrade cmake -y --limit-output --no-progress
 cmake --version
 
 cmake .. ^