Duplicate error messages have been fixed

test_suite/tests/compile-fail/remote/missing_field.rs

@@ -16,7 +16,7 @@ mod remote {
     }
 }
 
-#[derive(Serialize, Deserialize)] //~ ERROR: missing field `b` in initializer of `remote::S`
+#[derive(Serialize, Deserialize)]
 #[serde(remote = "remote::S")]
 struct S {
     a: u8, //~^^^ ERROR: missing field `b` in initializer of `remote::S`