revert seq len in multipack sampler

src/axolotl/utils/samplers/multipack.py

@@ -160,24 +160,19 @@ class MultipackBatchSampler(BatchSampler):
             for i in range(0, len(batches), self.batch_size)
         ]
 
-        seq_lens = [
-            [[lengths[idx] for idx in sub_batch] for sub_batch in batch]
-            for batch in batches
-        ]
-
         # statistics
         if set_stats:
             self.eff_total_used += total_used
             self.eff_total_slots += total_slots
 
-        return batches, seq_lens
+        return batches
 
     def __iter__(self):
-        batches, _ = self.generate_batches(set_stats=True)
+        batches = self.generate_batches(set_stats=True)
         return iter(batches)
 
     def num_batches(self):
-        batches, _ = self.generate_batches(set_stats=True)
+        batches = self.generate_batches(set_stats=True)
         return len(batches)
 
     def efficiency(self):