[caffe2] replace refernces to np.asscalar (#121332) (#121545)
Summary:
`np.asscalar` was deprecated and removed in a recent Numpy. It used to be implemented the following way, and the recommended alternative is to call `item()` directly:
```python
def asscalar(a):
return a.item()
```
This fixes all of the references.
Test Plan: visual inspection and automated tests
Differential Revision: D54697760
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121545
Approved by: https://github.com/malfet
