[api] Promote ExternalOneByteStringResourceImpl to DEPRECATED

R=yangguo@chromium.org

Bug: v8:8238
Change-Id: I37acbc2b7f14d16a57a27cc235769f8a7c18e3a1
Reviewed-on: https://chromium-review.googlesource.com/c/1349232Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57784}

include/v8.h

@@ -6265,7 +6265,7 @@ class V8_EXPORT AccessorSignature : public Data {
 
 
 // --- Extensions ---
-V8_DEPRECATE_SOON("Implementation detail", class)
+V8_DEPRECATED("Implementation detail", class)
 V8_EXPORT ExternalOneByteStringResourceImpl
     : public String::ExternalOneByteStringResource {
  public: