Update no trainer scripts for multiple-choice (#18468)

* swag_no_trainer updated for with gather_metrics

* Removed unused variable samples_seen

examples/pytorch/multiple-choice/run_swag_no_trainer.py

@@ -592,19 +592,11 @@ def main():
                 break
 
         model.eval()
-        samples_seen = 0
         for step, batch in enumerate(eval_dataloader):
             with torch.no_grad():
                 outputs = model(**batch)
             predictions = outputs.logits.argmax(dim=-1)
-            predictions, references = accelerator.gather((predictions, batch["labels"]))
-            # If we are in a multiprocess environment, the last batch has duplicates
-            if accelerator.num_processes > 1:
-                if step == len(eval_dataloader) - 1:
-                    predictions = predictions[: len(eval_dataloader.dataset) - samples_seen]
-                    references = references[: len(eval_dataloader.dataset) - samples_seen]
-                else:
-                    samples_seen += references.shape[0]
+            predictions, references = accelerator.gather_for_metrics((predictions, batch["labels"]))
             metric.add_batch(
                 predictions=predictions,
                 references=references,