Rollup merge of #130250 - compiler-errors:useless-conversion, r=jieyouxu

Fix `clippy::useless_conversion`

Self-explanatory. Probably the last clippy change I'll actually put up since this is the only other one I've actually seen in the wild.

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -883,7 +883,6 @@ where
             .into_iter()
             .chain(a_data.principal_def_id().into_iter().flat_map(|principal_def_id| {
                 elaborate::supertrait_def_ids(self.cx(), principal_def_id)
-                    .into_iter()
                     .filter(|def_id| self.cx().trait_is_auto(*def_id))
             }))
             .collect();