Some methods mix the usage of numpy and torch

[ydshieh]

Describe the bug

Here are what I find in resnet.py (not checking other files at this moment).

Goal: replace this with pure torch methods

• FirUpsample2D._upsample_2d
• FirDownsample2D. _downsample_2d
• upsample_2d
• downsample_2d

[patrickvonplaten]

Thanks a lot for opening this, we should indeed make those pure PyTorch functions