remove conflicting default impl

tests/simple.rs

@@ -31,6 +31,14 @@ struct Config {
     sub_config: SubConfig,
 }
 
+/// Config with default derive and default field
+#[config]
+#[derive(Default)]
+struct _DefaultConfig {
+    #[config(default)]
+    field: i32,
+}
+
 #[rstest]
 #[case(0, ["skipped"])]
 #[case(1, ["min"])]