Remove unhelpful bart warning (#7391)

src/transformers/modeling_bart.py

@@ -550,13 +550,8 @@ class BartDecoder(nn.Module):
         positions = self.embed_positions(input_ids, use_cache=use_cache)
 
         if use_cache:
-            if input_ids.shape[1] != 1 or past_key_values is None:
-                # if you make this an AssertionError, test_benchmark breaks.
-                warnings.warn("pass decoder_past_key_value_states to use_cache")
-
             input_ids = input_ids[:, -1:]
-            positions = positions[:, -1:]  # happens after we embed them
-            # assert input_ids.ne(self.padding_idx).any()
+            positions = positions[:, -1:]
 
         x = self.embed_tokens(input_ids) * self.embed_scale
         x += positions