[generate] do_sample default back to False (#3298)

* change do_samples back

* None better default as boolean

* adapt do_sample to True in test example

* make style

examples/summarization/bart/evaluate_cnn.py

@@ -35,7 +35,6 @@ def generate_summaries(lns, out_file, batch_size=8, device=DEFAULT_DEVICE):
             min_length=min_length + 1,  # +1 from original because we start at step=1
             no_repeat_ngram_size=3,
             early_stopping=True,
-            do_sample=False,
             decoder_start_token_id=model.config.eos_token_ids[0],
         )
         dec = [tokenizer.decode(g, skip_special_tokens=True, clean_up_tokenization_spaces=False) for g in summaries]