undo change in lod_tensor.md

Author: kexinzhao

doc/fluid/design/concepts/lod_tensor.md

@@ -189,23 +189,3 @@ and the <2,0>-slice of above slice is
 10  12
   ||
 ```
-
-## Length Representation vs Offset Representation
-
-The offset representation is an implementation-oriented decision and it makes understanding the idea behind LoDTensor difficult.
-Hence, we encapsulate this implementation detail in C++ and expose the original length representation in our Python API. 
-
-Specifically, user can use the following code to set or get the LoD info of a LoDTensor in Python:
-```Python
-# lod using length representation
-lod = [[1, 3, 2]]
-# Create a LoDTensor that has the above lod info.
-# This lod will be converted to an offset representation in the C++ implementation under the hood.
-tensor = fluid.LoDTensor(lod)
-
-# Set/Change the lod info of LoDTensor
-tensor.set_lod([[3, 1, 2]])
-# Get the lod info of a LoDTensor (the offset representation stored in C++ will be converted 
-# back to length representation), new_lod = [[3, 1, 2]]
-new_lod = tensor.lod()
-```