MetalBackend.h: Remove dead declarations

BUG=

Change-Id: Iaa19701a9fd0299db027917f7053fc50e18c6bf8
Reviewed-on: https://dawn-review.googlesource.com/c/3340
Reviewed-by: Stephen White <senorblanco@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/include/dawn_native/MetalBackend.h b/src/include/dawn_native/MetalBackend.h
index 758868d..0808957 100644
--- a/src/include/dawn_native/MetalBackend.h
+++ b/src/include/dawn_native/MetalBackend.h
@@ -24,8 +24,6 @@
 
 namespace dawn_native { namespace metal {
     DAWN_NATIVE_EXPORT dawnDevice CreateDevice(id<MTLDevice> metalDevice);
-    DAWN_NATIVE_EXPORT void SetNextDrawable(dawnDevice device, id<CAMetalDrawable> drawable);
-    DAWN_NATIVE_EXPORT void Present(dawnDevice device);
 }}  // namespace dawn_native::metal
 
 #endif  // DAWNNATIVE_METALBACKEND_H_