Remove use_peft parameter from training script

Instead we make the PEFT config optional which has the same effect.

src/lerobot/configs/train.py

@@ -63,8 +63,7 @@ class TrainPipelineConfig(HubMixin):
     scheduler: LRSchedulerConfig | None = None
     eval: EvalConfig = field(default_factory=EvalConfig)
     wandb: WandBConfig = field(default_factory=WandBConfig)
-    use_peft: bool = False
-    peft: PeftConfig = field(default_factory=PeftConfig)
+    peft: PeftConfig | None = None
 
     def __post_init__(self):
         self.checkpoint_path = None

src/lerobot/scripts/lerobot_train.py

@@ -247,7 +247,7 @@ def train(cfg: TrainPipelineConfig):
         ds_meta=dataset.meta,
     )
 
-    if cfg.use_peft:
+    if cfg.peft is not None:
         logging.info("Using PEFT! Wrapping model.")
         policy = wrap_policy_in_peft_model(cfg, policy)