remove in_reply_to in error constructor arg

src/protocol.rs

@@ -103,9 +103,8 @@ impl Body {
         b
     }
 
-    pub fn error(code: ErrorCode, in_reply_to: u64, text: Option<&str>) -> Self {
+    pub fn error(code: ErrorCode, text: Option<&str>) -> Self {
         Body {
-            in_reply_to,
             typ: "error".to_string(),
             code: Some(code),
             text: text.map(|t| t.to_string()),