[BE] remove unused value "max_seq_len" (#585)

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* __->__ #585

Author: XilunWu

torchtitan/models/llama/model.py

@@ -29,7 +29,6 @@ class ModelArgs:
     norm_eps: float = 1e-5
     rope_theta: float = 10000
 
-    max_batch_size: int = 32
     max_seq_len: int = 2048
     # If `True`, then each transformer block init uses its layer ID, and if
     # `False`, each uses the total number of transformer blocks