delete torch.nn.functional

[cjfghk5697]

I find useless import in Latent diffusion model
Therefore, I delete import torch.nn.functional.

Before :

import torch
import torch.nn as nn
import torch.nn.functional

After :

import torch
import torch.nn as nn

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Additionally, I find more unnecessary import in the unet.py. I delete and replace code.

import torch
import torch as th #This code have used one time. 
x = th.cat([x, x_input_block.pop()], dim=1)

x = torch.cat([x, x_input_block.pop()], dim=1) #Therefore, I delete the code, and replcae th.cat -> torch.cat.