pw_rpc: Add missing @Deprecated annotation

Change-Id: Ida81f2bc71bc617eb95d89d166138f5e9a53e040
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/94928
Pigweed-Auto-Submit: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Anthony DiGirolamo <tonymd@google.com>
diff --git a/pw_rpc/java/main/dev/pigweed/pw_rpc/MethodClient.java b/pw_rpc/java/main/dev/pigweed/pw_rpc/MethodClient.java
index 5986702..66c602c 100644
--- a/pw_rpc/java/main/dev/pigweed/pw_rpc/MethodClient.java
+++ b/pw_rpc/java/main/dev/pigweed/pw_rpc/MethodClient.java
@@ -84,6 +84,7 @@
   /**
    * @deprecated The request argument is deprecated and unused. Use the single-argument version.
    */
+  @Deprecated
   public Call openUnary(MessageLite unusedRequest, StreamObserver<? extends MessageLite> observer) {
     checkCallType(Method.Type.UNARY);
     return StreamObserverCall.open(rpcs(), rpc(), observer);