No need for torch-sparse-old now

[fengh16]

It seems that newer version of torch-sparse (I used the version 0.6.7) has the proper backward function and there is no need to install torch-sparse-old. (Actually I failed to install it.) After replacing torch-sparse-old with torch-sparse I successfully run the code.

There are the package versions I used:

torch                     1.10.2
torch-cluster             1.5.7
torch-geometric           2.0.3
torch-scatter             2.0.5
torch-sparse              0.6.7
torch-spline-conv         1.2.0