Remove double reference in Shell::print_json (#15460)

`obj` is already `&T`.

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Author: weihanglo

src/cargo/core/shell.rs

@@ -400,7 +400,7 @@ impl Shell {
 
     pub fn print_json<T: serde::ser::Serialize>(&mut self, obj: &T) -> CargoResult<()> {
         // Path may fail to serialize to JSON ...
-        let encoded = serde_json::to_string(&obj)?;
+        let encoded = serde_json::to_string(obj)?;
         // ... but don't fail due to a closed pipe.
         drop(writeln!(self.out(), "{}", encoded));
         Ok(())