Converted future-compatibility warning lint to regular lint.

See <#55994 (comment)> for details.

Author: Alexander Regueiro

src/librustc_lint/lib.rs

@@ -336,11 +336,6 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
             reference: "issue #52234 <https://github.com/rust-lang/rust/issues/52234>",
             edition: None,
         },
-        FutureIncompatibleInfo {
-            id: LintId::of(DUPLICATE_AUTO_TRAITS_IN_TRAIT_OBJECTS),
-            reference: "issue #56522 <https://github.com/rust-lang/rust/issues/56522>",
-            edition: None,
-        },
     ]);
 
     // Register renamed and removed lints.