simplify HandleCommandResponse (#11)

chief_of_state/v1/writeside.proto

@@ -36,24 +36,8 @@ message HandleCommandRequest {
 
 // HandleCommandResponse
 message HandleCommandResponse {
-  oneof response_type {
-    // With this response type an event is persisted before
-    // a reply is sent back to the caller. The reply message that is sent after
-    // the event is persisted contains the resulting state after the event is
-    // handled
-    PersistAndReply persist_and_reply = 1;
-    // With this response the current state is sent back to the caller.
-    // This type of response is very useful to read-only requests that do not
-    // need a read side query.
-    Reply reply = 2;
-  };
-}
-// Reply results in current state to be returned
-message Reply {}
-
-// PersistAndReply contains the event to persist
-message PersistAndReply {
-  // event to persist
+  // An event to append to the journal. If not set, COS
+  // will treat this command as a no-op.
   google.protobuf.Any event = 1;
 }