fix layer norm when torch>=1.12 (#1168)

mmdeploy/pytorch/ops/layer_norm.py

@@ -2,7 +2,6 @@
 # Modified from:
 # https://github.com/pytorch/pytorch/blob/9ade03959392e5a90b74261012de1d806cab2253/torch/onnx/symbolic_opset9.py
 
-import torch
 from torch.onnx.symbolic_helper import parse_args
 
 from mmdeploy.core import SYMBOLIC_REWRITER
@@ -22,17 +21,6 @@ def layer_norm__default(ctx, g, input, normalized_shape, weight, bias, eps,
     """
     import torch.onnx.symbolic_helper as sym_help
     from torch.onnx.symbolic_opset9 import add, mul, pow, sqrt, sub
-    if sym_help._operator_export_type == \
-            torch.onnx.OperatorExportTypes.ONNX_ATEN_FALLBACK:
-        return g.op(
-            'ATen',
-            input,
-            weight,
-            bias,
-            normalized_shape_i=normalized_shape,
-            eps_f=eps,
-            cudnn_enable_i=cudnn_enable,
-            operator_s='layer_norm')
 
     axes = [-i for i in range(len(normalized_shape), 0, -1)]