tutorials are broken due to `AsDiscrete` and `AsDiscreteD` updates

[wyli]

Describe the bug
the recent update of AsDiscrete and AsDiscreteD break many tutorials,
this should be rectified accordingly

see also Project-MONAI/MONAI#3352.

[wyli]

@yiheng-wang-nv, could you please look into this?

[yiheng-wang-nv]

Hi @wyli , sure. I was busy on other tasks, and now I'm able to start to update the related tutorials.