Ty FnSigs no longer have the variadic param

As of commit a88d181a023e in rustc, HIR and Ty level IR no longer carries the
variadic dummy param, so we don't need to subtract 1 from the number of
arguments.

Author: rinon

c2rust-refactor/src/illtyped.rs

@@ -140,10 +140,8 @@ impl<'a, 'tcx, F: IlltypedFolder<'tcx>> MutVisitor for FoldIlltyped<'a, 'tcx, F>
             ExprKind::Call(_callee, args) => {
                 if let Some(fn_sig) = opt_fn_sig {
                     for (i, arg) in args.iter_mut().enumerate() {
-                        if !fn_sig.c_variadic || i < fn_sig.inputs().len() - 1 {
-                            if let Some(&ty) = fn_sig.inputs().get(i) {
-                                illtyped |= self.ensure(arg, ty);
-                            }
+                        if let Some(&ty) = fn_sig.inputs().get(i) {
+                            illtyped |= self.ensure(arg, ty);
                         }
                     }
                 }