refactor: use @ObsoleteApi instead of @deprecated for TracedUnaryCallable constructor

Author: blakeli0

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/tracing/TracedUnaryCallable.java

@@ -33,6 +33,7 @@
 import com.google.api.core.ApiFutures;
 import com.google.api.core.BetaApi;
 import com.google.api.core.InternalApi;
+import com.google.api.core.ObsoleteApi;
 import com.google.api.gax.rpc.ApiCallContext;
 import com.google.api.gax.rpc.ResourceNameExtractor;
 import com.google.api.gax.rpc.UnaryCallable;
@@ -56,7 +57,7 @@ public class TracedUnaryCallable<RequestT, ResponseT> extends UnaryCallable<Requ
 
 
 
-  @Deprecated
+  @ObsoleteApi("Use constructor with ApiTracerContext instead")
   public TracedUnaryCallable(
       UnaryCallable<RequestT, ResponseT> innerCallable,
       ApiTracerFactory tracerFactory,