Do you have any other torchvision or PyTorch installations on this machine and environment?
I just tried to reproduce the import issue by installing PyTorch 1.7.0 and torchvision==0.8.1 as the CPU-only packages in a new conda env via:
conda install pytorch torchvision torchaudio cpuonly -c pytorch

and I can import torchvision:
>>> import torch
>>> torch.__version__
'1.7.0'
>>> import torchvision
>>> torchvision.__version__
'0.8.1'