improve lora+ impl.

Former-commit-id: 332bad25455a70ad9204e7dd384bb086d789aa39

src/llmtuner/model/loader.py

@@ -109,10 +109,6 @@ def load_model(
 
     if not is_trainable:
         model.requires_grad_(False)
-        if not getattr(model, "quantization_method", None):
-            for param in filter(lambda p: p.device.type == "cuda", model.parameters()):
-                param.data = param.data.to(model_args.compute_dtype)
-
         model.eval()
     else:
         model.train()