onnx-simplifier简化时不合并concat

ref: https://github.com/daquexian/onnx-simplifier/issues/94#issuecomment-706077511

run onnxsim with --skip-optimizer fuse_consecutive_concats

example:

python -m onnxsim --skip-optimizer fuse_consecutive_concats  your.onnx your_simplified.onnx