use the correct feature gate

Co-authored-by: Boxy <supbscripter@gmail.com>

compiler/rustc_typeck/src/outlives/implicit_infer.rs

@@ -120,7 +120,7 @@ fn insert_required_predicates_to_be_wf<'tcx>(
     // Luckily the only types contained in default substs are type
     // parameters which don't matter here.
     //
-    // FIXME(const_param_types): Once complex const parameter types
+    // FIXME(adt_const_params): Once complex const parameter types
     // are allowed, this might be incorrect. I think that we will still be
     // fine, as all outlives relations of the const param types should also
     // be part of the adt containing it, but we should still both update the