[api] Advance CreateDefaultPlatform deprecation

Change platform::CreateDefaultPlatform from V8_DEPRECATE_SOON to
V8_DEPRECATED.

Bug: v8:8562
Change-Id: I053ff29b27dcd454960007bfd6597a01e1b2e62a
Reviewed-on: https://chromium-review.googlesource.com/c/1411636Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58831}

include/libplatform/libplatform.h

@@ -41,7 +41,7 @@ V8_PLATFORM_EXPORT std::unique_ptr<v8::Platform> NewDefaultPlatform(
         InProcessStackDumping::kDisabled,
     std::unique_ptr<v8::TracingController> tracing_controller = {});
 
-V8_PLATFORM_EXPORT V8_DEPRECATE_SOON(
+V8_PLATFORM_EXPORT V8_DEPRECATED(
     "Use NewDefaultPlatform instead",
     v8::Platform* CreateDefaultPlatform(
         int thread_pool_size = 0,