build: Cleanup build_windows_targets.bat
build: Cleanup build_windows_targets.bat

- This batch file can be run in any of the three repos,
  Vulkan-LoaderAndValidationLayers, VulkanTools, and VulkanSamples,
  so remove comments suggesting otherwise.
- Replace spot-check for an artifact with checking errorlevel
  from msbuild to discover build failures.

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools