Auto merge of #118297 - shepmaster:warn-dead-tuple-fields, r=WaffleLapkin

Merge `unused_tuple_struct_fields` into `dead_code`

This implicitly upgrades the lint from `allow` to `warn` and places it into the `unused` lint group.

[Discussion on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Moving.20.60unused_tuple_struct_fields.60.20from.20allow.20to.20warn)

library/std/src/collections/hash/set/tests.rs

@@ -352,7 +352,7 @@ fn test_replace() {
     use crate::hash;
 
     #[derive(Debug)]
-    struct Foo(&'static str, i32);
+    struct Foo(&'static str, #[allow(dead_code)] i32);
 
     impl PartialEq for Foo {
         fn eq(&self, other: &Self) -> bool {