Vulkan: Don't use vulkan.h's prototypes.

VulkanFunctions handles the storing of Vulkan function pointers so Dawn
doesn't need the declarations for Vulkan entrypoints.

Bug: dawn:269

Change-Id: I25f05d4a82fd31a60b22257261e940ce276f5eac
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/17960
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/common/vulkan_platform.h

@@ -143,6 +143,7 @@ namespace dawn_native { namespace vulkan {
         }                                                                           \
     }  // namespace dawn_native::vulkan
 
+#define VK_NO_PROTOTYPES
 #include <vulkan/vulkan.h>
 
 // Redefine VK_NULL_HANDLE for better type safety where possible.